Feather Fiber-Based Thermoplastics: Effects of Different Plasticizers on Material Properties

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Feather Fiber-Based Thermoplastics: Effects ofDifferent Plasticizers on Material Properties

Aman Ullah, Jianping Wu*

Poultry feather fiber is transformed into biothermoplastics using a twin screw extruder, andthe plasticizing effect of four different plasticizers on the material properties is investigated.Conformational changes, viscoelastic behavior, thermal degradation, and phase transitionsare assessed by means of FTIR spectroscopy, DMA,TGA, and DSC, respectively. The mechanical prop-erties of the plasticized resins are assessed bytensile measurements, while optical transmit-tance is recorded using UV-Vis spectropho-tometry. The water uptake behavior of the fiberkeratin and plasticized resins is also investigated.

1. Introduction

After their birth in the beginning of 20th century, synthetic

polymers have been growing tremendously due to avail-

ability of large number of cheap chemicals, suitable for the

production of a variety of durable macromolecular

materials.[1] In addition to remarkable and progressive

increase in prices, the distinct durability of the petro-

plastics which makes them ideal for several applications, is

now leading to waste disposal problems, as these materials

are not biodegradable.[2] Due to these facts, the develop-

ment of biodegradable and environment-friendly bioplas-

tic materials from renewable resources has attracted

increasing attention, as means to substitute petroleum-

based plastic materials, which present several concerns in

terms of environmental pollution and sustainability.[3–5]

Renewable resources, because of their pervasive character,

are inherently valuable in this domain and may provide

sustainability with respect to polymeric materials, espe-

cially attention has now been focused on the utilization of

by-products from agricultural, forestry, agronomy, and

marine activities for producing new polymeric materials

Dr. A. Ullah, Prof. J. WuDepartment of Agricultural, Food and Nutritional Science,University of Alberta, Edmonton, Alberta T6G 2P5, CanadaE-mail: [email protected]

� 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlin

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instead of using food resources or other natural materials.[1]

One of such examples is poultry feathers, which are

ineluctably produced in large quantities as byproduct of the

poultry industry. It is estimated that more than 4 billion

pounds of feathers are annually generated as a byproduct of

poultry industry in the United States[6] and more than 157

million pounds in Canada. Currently, in addition to animal

feed, and very limited use of feathers in industrial

applications[6,7] the major part of the poultry feathers is

disposed in landfills.

Feather contains about 90% protein called keratin.

Feather keratin is biodegradable, renewable, and poten-

tially valuable biopolymer. Feather consists of 50 wt% fiber

and 50 wt% quill. Quill fraction is composed of more b-sheet

than a-helix while the feather fiber has a higher percentage

of a-helix compared to b-sheet.[8] Utilization of this

valuable biomass will not only be beneficial for poultry

industry, but will also reduce health hazards, and benefit

the environment, by reducing solid wastes being sent to

landfills.[9]

In the recent years, some efforts have been made to

modify poultry feather fibers, either by surface grafting of

synthetic polymers or blending with plasticizer, to trans-

form them into films by using casting or compression

molding techniques. Native chicken feather fiber was

modified by grafting methyl acrylate, using K2S2O8/

NaHSO3 as redox system and films were prepared by

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Table 1. Carbon numbers, molecular weights, and boiling pointsof the plasticizers used.

Plasticizer Carbon

number

Molecular

weight

[g mol�1]

Boiling

point

[-C]

ethylene glycol 2 62 197

propylene glycol 3 76.09 188

glycerol 3 92 290

diethyl tartrate 8 206.19 280

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A. Ullah, J. Wu

compression molding of grafted feathers with glycerol as a

plasticizer.[10] Authors reported higher tensile properties

than soy protein isolate (SPI) and starch acetate (SA) based

films. Schrooyen and coworkers carboxymethylated

extracted feather keratin and prepared films by casting

blends of modified keratin with various amounts of

glycerol.[11] Avian feather keratin-based films, prepared

by compression molding without reducing or oxidizing

agents were developed by Barone et al.[12] Observed elastic

modulus, stress at break, and strain at break values were

40–500 MPa, 6–15 MPa, and 8–50%, respectively. The effect

of different barrel and die temperatures on the extrusion of

feather keratin, using glycerol, water, and sodium sulfite as

processing aids was also investigated.[13] Authors observed

that when lower barrel and die temperatures were used,

keratin polymer softened just before the die, leading to

higher viscosities. On the contrary, while using high barrel

temperatures polymer softened earlier inside the barrel

leading to lower apparent viscosities.

Due to a variety of intermolecular interactions, proteins

generally have softening temperatures either very close or

above their decomposition temperatures.[14] Therefore, for

successful processing of proteins and to control protein/

protein interactions, the addition of plasticizer is required. A

plasticizer is a small molecule substantially of low volatility

and high boiling point which, when added to polymeric

material, changes certain physical and chemical properties

of that material.[15] Several theories, including ‘‘lubricity

theory,’’ ‘‘gel theory,’’ and ‘‘free volume theory,’’ have been

proposed about the mechanism of plasticizer action.[16]

Without going into details, which theory is most felicitous,

the plasticizers being small molecules improve processa-

bility by interposing themselves into the polymer chains

and altering the forces holding the chains together.[17]

Water and glycerol are the most commonly studied

plasticizers of keratin and other proteins; even chemically

modified keratin needs glycerol as plasticizer to develop

thermoplastics.[10,18] However, it has been noted that water

and glycerol are unstable and migration of these plastici-

zers during storage of protein-based plastics have been

reported.[19] In addition, glycerol increases moisture

sensitivity, and significantly reduces tensile properties,

especially at high humidities.[20,21]

In present work feather fiber keratin was extruded, using

30% of various possible plasticizers. Poly(ethylene glycol)

(PEG 200 and PEG 500), sorbitol, lactic acid, ethylene glycol

(EG), propylene glycol (PG), glycerol, and diethyl tartrate

(DET). However, no cohesive blends were obtained in the

presence of PEG, sorbitol, and lactic acid, showing that these

components were ineffective as plasticizers for fiber keratin

therefore these materials were not considered as suitable

materials for detailed study. The efficient plasticizers

adopted for the study were, EG, PG, glycerol, and DET.

The objectives were first, to investigate the effect of these

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plasticizers on the structural, thermal, mechanical, and

viscoelastic properties of fiber keratin-based resins, and

then to explore effects of these plasticizers on the water

sensitivity of the fiber-based bioplastics.

2. Experimental Section

2.1. Materials

EG (Sigma-Aldrich, 99þ%), PG (Aldrich, 99.5%), glycerol (Sigma,

99þ%), DET (Aldrich, 99þ%), sodium sulfite (Sigma-Aldrich,

98þ%, MW¼126.04 g �mol�1), and petroleum ether ACS reagent

(Sigma-Aldrich, 99.5%, boiling range 30–60 8C) were used as received.

The main properties of the plasticizers are given in Table 1, and

chemical structures of the plasticizers are shown in Figure 1.

2.2. Fiber Processing

White chicken feathers from broilers supplied by the Poultry

Research Centre (University of Alberta) were washed several times

with soap (Palmolive, antibacterial) and with a plenty of hot water.

The cleaned feathers were dried by first spreading under a closed

fume hood for 4 d to evaporate water and then in a ventilated oven

at 50 8C for 8 h to completely remove remaining moisture. The

cleaned and dried feathers were processed with scissors, and the

fiber portion was separated from the quill portion. Fiber was

ground using a Fritsch cutting mill (Pulverisette 15, Laval Lab. Inc.,

Laval, Canada), at a sieve insert size of 0.25 mm. The batches of

ground fiber material (30 g each) were then treated in a Soxhlet

(extraction tube with 50 mm internal diameter) for 4 h with 250 mL

of petroleum ether to remove grease. The petroleum ether was

evaporated and the dried fiber was stored at room temperature

until used.

2.3. Sample Preparation and Extrusion

Blends of ground fiber with selected plasticizers, [including EG, PG,

glycerol (G), and DET], and sodium sulfite were prepared in a

Laboratory heavy duty blender (Waring Commercial, 120 volt,

Torrington, CT, USA). In a typical blend, 70 g of fiber, 30 g of

plasticizer, and 3 g of sodium sulfite were used. Sodium sulfite was

added into the system in order to dissociate disulfide bonds

between the cysteine residues of the keratin chains to achieve

efficient mixing among keratin and plasticizers. Desired amounts

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(a) (b)

(c) (d)

Figure 1. Chemical structure of (a) EG, (b) PG, (c) glycerol, and (d) DET.

Feather Fiber-Based Thermoplastics: Effects of Different Plasticizers . . .

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of fiber, plasticizer, and sodium sulfite were mixed in a blender at

high speed (2200 rpm) for 20 min; with 1 min break (for removing

the material stuck to the blender walls) after every 3 min blending.

These blends were sealed in plastic bags and placed at room

temperature overnight so that plasticizers could sufficiently

incorporate into the ground fiber material.

Extrusion was performed using a twin screw extruder (Plasti-

corder Digi-system, PL 2200, Brabender Instruments, Inc South

Hackensack, NJ, USA). The screws were single flighted and had

uniform pitch. The barrel length was 35 cm with a diameter of 31.8/

20 mm. A 7 mm die was used. Extrusion was accomplished at

temperatures of 90, 100, 110, 120, and 120 8C, as well as a screw

speed of 50 rpm. After extrusion, samples were cut and cooled to

room temperature.

2.4. Film Preparation

Films of plasticized materials, for mechanical testing, optical

transmittance measurements, and water uptake (WU) studies were

prepared by compression molding the resins for 5 min at 110 8C and

3500 psi pressure using a Carver press (model 3851-0, Wabash,

IN, USA).

2.5. Fourier-Transform Infrared (FTIR) Spectroscopy

FTIR spectra of solid samples in KBr pellets were obtained on an FTIR

spectrophotometer (Thermo Nicolet 750, Madison, WI, USA). Very

thin slices of extrudates were cut and equilibrated at 0% relative

humidity in a desiccator containing P2O5 for 2 weeks prior to FTIR

investigation. The spectra were collected within the frequency

range 4000–400 cm�1. All sample spectra were recorded at 32 scans

and 4 cm�1 resolution, and spectra of two replicate measurements

for each sample were averaged. The infrared spectra were acquired

using Thermo Scientific OMNIC software package (version 7.1).

Second derivative was used to locate the positions of peaks in amide

I region.

2.6. DSC and Thermogravimetric Analysis (TGA)

DSC was performed under a continuous nitrogen purge on a Perkin-

Elmer (Pyris 1, Norwalk, CT, USA), calorimetric apparatus. The

instrument heat flow and temperature were calibrated using a

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Macromol. Mater. Eng. 2012, DO



sample of pure indium. Samples having a mass of (�5 mg) were

scanned at 10 8C �min�1 from 25 to 275 8C.

TGA was performed on a Perkin-Elmer (Pyris 1, Waltham, MA,

USA), thermogravimetric analyzer. About 10 mg of the sample was

heated at 10 8C �min�1 over a temperature range of 25–600 8Cunder a nitrogen atmosphere.

2.7. Dynamic Mechanical Analysis (DMA)

A dynamic mechanical analyzer Perkin-Elmer (DMA 8000, Wal-

tham, MA, USA) was used to measure dynamic mechanical

properties in tensile mode at an oscillatory frequency of 1 Hz with

an applied deformation of 0.05 mm during heating. Analyses

were performed on rectangular specimens dimensions of

�11� 6� 0.8 mm (length�width� thickness). The exact thick-

ness and width of the samples was measured with digital calipers

at three different places and averages were used. Each sample was

analyzed at least in duplicate. Temperature scans between 0 and

160 8C were performed at 2 8C �min�1 heating rate. Specimens were

equilibrated (2 weeks) at 0% relative humidity in a desiccator

containing P2O5 prior to analysis. The storage modulus (E0) and tan d

(E00/E0) were recorded as a function of temperature.

2.8. Tensile Tests

Mechanical properties (tensile strength, breaking elongation, and

Young’s modulus) of the films were determined at room

temperature on an Instron 5967 (Norwood, MA, USA) equipped

with a 50 N load cell at a crosshead speed of 50 mm �min�1. The data

for each sample were obtained from an average of testing at least

five specimens with an effective length of 80 and width of 10 mm.

2.9. Water Uptake

Water absorption behavior of the fiber keratin and the plasticized

materials was determined by using controlled humidity and

temperature chamber ETS 5518 (Glenside, PA, USA). Rectangular

specimens of �10�6�1 mm (length�width� thickness) were

conditioned at 0% relative humidity in a desiccator with P2O5 as

desiccant at room temperature until constant weight of films was

reached which was termed as an initial weight (W0). The moisture

content of the sheets was determined by conditioning the samples

at 25 8C and 98% relative humidity in controlled environment

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chamber. The specimens from the chamber were removed at

specific intervals and weighed on a five digit balance to obtain the

weight Wt. The WU of the specimens was determined using[22]

Figpladatcla

rly V

WUð%Þ ¼Wt �Wo

Wo� 100 (1)

2.10. Optical Transmittance

Transparency of the plasticized materials was determined by using

a UV-Vis spectrophotometer Evolution 60S (Thermo Scientific,

Nepean, ON, USA). Films of 1 mm thickness were cut into

rectangular shapes and placed on the internal side of spectro-

photometer cell. The transmittance (%) was measured using

wavelength between 250 and 800 nm at 5 nm intervals. Air was

used as blank (100% transmittance). Duplicate measurements were

performed with individually prepared films and average transmit-

tance (%) values were plotted against wavelength.

3. Results and Discussion

3.1. Conformational Changes

FTIR investigation can be used as an effective tool to assess

the structural changes in proteins. In Figure 2, the IR spectra

of fiber and plasticized resins exhibit typical amide

vibrations including amide A (N�H stretching,

3300 cm�1), amide I (C¼O stretching, with a minor

contribution from N�H bending and C�N stretching,

1600–1700 cm�1), amide II and amide III (N�H bending

and C�N stretching, at around 1540 and 1240 cm�1,

respectively).[23,24] Significant changes can be seen in

amide A region of resins formed with different plasticizers.

A broad absorption band of neat fiber keratin appearing at

3307 cm�1 (Figure 2A) is mainly due to hydrogen bonded

N�H stretching vibrations,[25] as in native secondary

ure 2. FTIR spectra of (A) fiber, (B) EG plasticized, (C) PGsticized, (D) glycerol plasticized, and (E) DET plasticized extru-es. Spectra are offset and curves are shifted vertically for

rity.



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structure the peptide N�H groups make hydrogen bonds

with amide C¼O groups. A shift in this band toward higher

wavenumbers as a function of plasticizer type has been

observed, which becomes sharp particularly in the presence

of glycerol and EG (Figure 2B and D). This shift to higher

wavenumbers can be attributed to the disruption of the

internal hydrogen bonds of the peptide groups by

plasticizers and formation of new bonds between protein

and plasticizers. Polyols disrupt internal hydrogen bonds of

proteins by making new hydrogen bonds between the O�H

groups of alcohol and N�H and C¼O groups of polypep-

tides.[26] It is also well known that the absorption peak due

to free O�H in alcohols appears at around 3600 cm�1, while

hydrogen bonded O�H groups absorb at lower wavenum-

bers between 3200 and 3500 cm�1.[27] The positions of these

bands reflect the strength and type of hydrogen bonding,

while another general characteristic of these hydrogen

bonds is that the stronger the hydrogen bond, the greater

the intensity of the corresponding peak.[28]

This trend in bonding was further confirmed by changes

in amide II region of the FTIR spectrum (Figure 3). The amide

II band is related with N�H bending and C�H stretching

vibrations. Although it is much less conformationally

sensitive than amide I, it is much more sensitive to the

environment of the N�H group.[29] Therefore, the amide II

band can be used to deduce changes to the environment of

the N�H groups and respond to differences in hydrogen

bonding environments.[30]

In general, stronger hydrogen bonded N�H groups

absorb at higher frequencies. As compared to the neat

fiber (Figure 3A), decrease in absorption intensity centered

Figure 3. Amide II region spectra of (A) fiber, (B) EG plasticized,(C) PG plasticized, (D) glycerol plasticized, and (E) DET plasticizedextrudates. For easier comparison, intensities have been normal-ized in all spectra at 1540 cm�1. Spectra are offset and curves areshifted vertically for clarity.

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at 1515 cm�1 can be seen in the presence of EG, PG, and

glycerol plasticizers (Figure 3B–D). However, the relative

intensity at 1540 cm�1 increases and this increase is more

prominent in the presence of EG. EG, consisting of a short

aliphatic chain capped with hydroxyl groups, can form

stronger hydrogen bonds with polypeptide chains, while

weaker hydrogen bonding of glycerol and PG with fiber

keratin compared to EG might actually be due to asym-

metric structures of these plasticizers. The lack of change in

the absorption band of DET (Figure 3E) may be due to its

inability to diffuse in and/or interact with polymer chains

because of less symmetry and longer chain length. It is

expected that as chain length increases, symmetry

decreases, and thus so does the hydrogen bonding.

Among all the amide bands of the backbone peptide

groups in proteins, the most intense and the most widely

used one is the amide I band. This band arises mainly from

the C¼O stretching vibration of the amide carbonyl group,

which is weakly coupled with the in-plane N�H bending

and the C�N stretching vibration and appears in the region

between �1700 and 1600 cm�1.

For the enhancement of resolution, techniques such as

second derivative[31] can be used to locate the positions of

individual amide I bands. This technique can be used as a

sensitive diagnostic tool in illustrating changes occurring in

the secondary structure. Since plasticized keratin is a

complex system, therefore broad absorption peaks appear

due to overlap of absorption bands of various components

with different contents. Usually, in order to amplify the

intricate differences in spectra, second derivative infrared

spectra are used.[32]

Figure 4 shows second-derivative FTIR spectra of neat

fiber and plasticized resins. For clarity, the spectra are

presented on an offset scale. As is evident, second derivative

analysis allowed the direct separation of amide I band into

Figure 4. Amide I region second derivative spectra of (A) neatfiber, (B) EG plasticized, (C) PG plasticized, (D) glycerol plasticized,and (E) DET plasticized extrudates.





its components and absorption bands in the original

spectrum are disclosed as negative bands in the second

derivative spectrum. The major component bands evi-

denced at 1636, 1653 and 1658, and 1662 cm�1 in neat fiber

and plasticized resins can be assigned to, b-sheets, a-helices,

and 310-helices, respectively.[33] While other peaks at 1675,

1680, and 1684 cm�1 can be attributed to antiparallel b-

sheets/aggregated strands.[34] Significant differences can

be seen between neat fiber keratin and extruded resins

particularly in EG and glycerol plasticized materials. The

decrease in intensity at 1662 and 1653 cm�1 compared to

neat fiber keratin (Figure 4A), and the appearance of new

peaks at 1630 and 1624 cm�1 (Figure 4B) in the EG

plasticized resin suggests that EG promotes the formation

of b-sheet structures at the expense of a-helices. Further-

more, a peak at 1624 cm�1 indicates the presence of

stronger intermolecular hydrogen bonds between fiber

keratin and EG which was also confirmed by sharp peak at

4313 cm�1 (Figure 2B). On the contrary, in case of EG and

glycerol plasticized resins (Figure 4C and D), increase in

intensities of peaks at 1662, 1658, and 1653 cm�1 and

relatively low intensities of peaks at 1630 and 1624 cm�1

compared to EG plasticized material suggests that these

plasticizers promote the formation of higher number of

helices (both a-helix and 310-helix) than b-sheet structures

and make complex interaction with keratin molecules.

3.2. Mechanical Properties

Stress/strain curves from tensile tests are commonly used

to characterize polymer properties. The properties typically

investigated are Young’s modulus E (tensile or elastic

modulus), tensile strength, and percent strain at break (%

elongation). Generally glassy materials have higher tensile

strength values (above 30 MPa) and are highly brittle

(almost no elongation). Materials having tensile strength

values lower than 5 MPa and elongation more than 100%

are considered as rubbery materials, while thermoplastic

materials (lying in the glass transition zone) have inter-

mediate properties.[35] Figure 5 shows the representative

stress/strain curves of extruded materials with different

plasticizers, while their tensile properties are summarized

in Table 2.

A common consensus is that hard and brittle polymers

exhibit high tensile modulus, moderate tensile strength,

and low elongation at break; soft and tough polymers are

characterized by low elastic modulus, moderate tensile

strength, and high percent elongation at break; and hard

and tough polymers are characterized by high elastic

modulus, high tensile strength, and high elongation at

break.[36] The pressed films of neat fiber material (without

plasticizer) were too brittle to perform mechanical testing.

It was observed that PG and DET plasticized materials

showed higher tensile modulus, moderate tensile strength

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Figure 5. The representative stress/strain curves of extrudatesplasticized with EG, PG, glycerol (G), and DET.

Figure 6. DSC heat flow signals of neat fiber material and extru-dates plasticized with different plasticizer.

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A. Ullah, J. Wu

but lower breaking elongation than both EG and glycerol

plasticized resins. Although, EG and glycerol plasticized

extrudates had no significant difference in tensile strength

but elongation at the break point of EG plasticized plastics

was almost more than five times higher than glycerol

plasticized resin. A general understanding is that a true

plasticizer generally increases the flexibility and extensi-

bility of the plasticized material while its interactions at a

molecular level increase tensile strength and stiffness. The

differences in mechanical properties especially % elonga-

tion might be due to differences in plasticization efficiency.

EG, the smallest molecule, has the greatest ability to reduce

polymer-polymer associations, increase free volume, and

interact with polypeptide chains through hydrogen bonds.

Glycerol, on the other hand, has three hydroxyl groups but

an asymmetric structure, therefore its interactions with

polypeptide chains may be more complex, which may

ultimately affect mechanical properties. Similar results

were observed while studying the influence of plasticizers

on properties of pea proteins.[37] The DET also has two free

hydroxyl groups but its ability to penetrate into polymer

chains and form hydrogen bonds with peptide groups

might be low due to both its highest molecular mass and the

presence of two bulky ethyl groups located at each end of

molecule, thus making it the least effective plasticizer.

Table 2. Comparison of tensile properties of extrudates with differe

Plasticizer Tensile strength

[MPa]

ethylene glycol 17.76� 2.08

propylene glycol 22.25� 1.52

glycerol 15.66� 4.24

diethyl tartrate 19.0� 3.74




3.3. Thermal Properties

The thermal transitions of the fiber keratin as well as

extruded materials plasticized by different plasticizers

were studied by DSC. Typical DSC thermograms of neat fiber

and extrudates are presented in Figure 6. Fiber keratin

material exhibited two transitions, a broad peak below

100 8C may be due to evaporation of residual moisture of the

protein and a small peak at around 235 8C might be due to

the crystalline melting of the fiber keratin.[12] The moisture

evaporation takes place slowly and gradually in the

presence of EG and glycerol, while absence of this peak

in the case of PG and DET might be due to the lower

hydrophilic nature of these plasticizers. Except DET

plasticized material, all other resins displayed a second

endothermic peak (attributed to melting) at temperature

lower than 275 8C. An endothermic peak can clearly be seen

at lower temperature in EG plasticized resin than other

plasticized materials, which demonstrates higher improve-

ment in thermoplasticity compared to other plasticizers.

More than one peaks observed in case of the glycerol

plasticized material might be due to different types of

interaction of glycerol with fiber keratin: a loosely bound

glycerol (glycerol-rich zones) and glycerol having higher

interactions with protein. Chen and Zhang also observed

nt plasticizers.

Elongation at break

[%]

Young’s modulus

[MPa]

43.8� 2.21 354.0� 10.2

7.6� 4.70 811.2� 46.2

8.5� 3.15 332.3� 11.4

3.3� 1.57 907.9� 91.1

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glycerol-rich and protein-rich domains, while studying

transitions and microstructures of glycerol plasticized soy

protein.[38]

3.4. Viscoelastic Properties

DMA measures the changes in the viscoelastic properties of

the polymers with changing temperature. Thermal transi-

tions are generally associated with chain mobility and the

most important of these transitions is the glass transition

(Tg), which is related to the onset of main chain motions.

Normally, DMA data for solids is displayed as storage

modulus and damping or tan d versus temperature. This

technique is very sensitive to the motions of the polymer

chains and it is a powerful tool for measuring transitions in

polymers. In order to display changes occurring over large

ranges, modulus is generally displayed on log scale. Figure 7

shows changes in storage modulus (A) and tan d (B) values

of fiber material plasticized with different plasticizers as

a function of temperature. The Tg values have been

determined from tan d versus temperature plots.

A clear shift in the onset of E’ drop to lower temperature

can be seen, particularly with EG and glycerol. This drop in E’

of EG and glycerol plasticized materials at Tg is similar to

the synthetic polymers (usually more than 3 orders of

magnitude).[39]

Figure 7. DMA thermograms log E0 (A), and tan d (B) for fibermaterial plasticized with EG, PG, glycerol (G), and DET.





The observation of a single, relatively narrow transition

and the strong plasticization effect of EG reflect a good

compatibility of this plasticizer with fiber keratin. This

strong plasticization effect can be attributed to the fact that

it has the low-molecular-weight as compared to all other

plasticizers investigated, having higher ability to lubricate

by incorporating itself among the polymer chains, and

the formation of polymer/plasticizer interactions at the

expense of polymer/polymer interactions. Its plasticization

efficiency is also reflected by significant depression in glass

transition as compared to other plasticizers, in agreement

with the free volume theory of the plasticization.[16]

According to this theory, the plasticizer efficiency is

predicted from the Tg depression of plasticized polymer.

It is also very interesting that a sharp decrease in the

rubbery modulus (Figure 7A) and increase in tan d peak size

(Figure 7B) is observed, in the presence of the EG as

plasticizer. As size of the tan d peak reflects the volume

fraction of the material undergoing transition, therefore,

from highest variation in E’ and tan d peak, it can be

suggested that EG plasticized material undergoes glass

transition phenomenon to greater extent and interactions

involved between keratin and EG are quite homogeneous.

Above the glass transition, E’ depends highly on the density

of the polymer crosslinks,[40] and it is expected that the

higher the density of polymer/polymer crosslinks the lower

the decrease in rubbery modulus. Therefore, the decrease in

the rubbery modulus and increase in tan d is actually due to

replacement of polymer/polymer crosslinks by polymer

plasticizer interactions.[41] For PG and DET, very broad

transitions (both a and tan d) suggest weaker interactions

between these plasticizers and the keratin molecules. Two

transitions in both the a-relaxation and tan d values of

glycerol plasticized material have been observed. These

may be assigned to glycerol-rich and protein-rich domains.

3.5. Thermal Stability

The TG and DTG curves of neat fiber and the plasticized

materials are shown in Figure 8. Two weight loss steps can

be seen in case of pristine fiber material. The weight loss in

the first stage (near 100 8C) for the neat fiber is assigned to

the evaporation of residual moisture whereas the second

step (between 250 and 600 8C) is mainly due to the

degradation of the fiber keratin. The degradation of each

plasticized resin consists of three weight loss steps. The first

gradual weight loss (below 150 8C) is due to the evaporation

of moisture, the second (between 150 and 250 8C) is

attributed to the plasticizer evaporation, and the final

weight loss beyond 250 8C is due to decomposition of fiber

material. It is important to mention here that plasticizers

act by reducing hydrogen bonding, van der Waals, or ionic

interactions that hold polymer chains together, through

forming plasticizer/polymer interactions,[42] by adding free

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Figure 8. (A) TG and (B) DTG; curves of neat quill material andplasticized resins. The DTG curves have been offset for clarity.

Figure 9. Water uptake (WU) behaviors of neat fiber and plasti-cized resins during conditioning at 98% RH versus time.

Table 3. Water uptake (WU) at equilibrium of fiber and plasticizedresins at 98% RH.

Sample Water uptake at equilibrium

[wt%]

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A. Ullah, J. Wu

volume to the system, causing a physical separation of

adjacent chains and by acting as lubricants between chains.

The temperature at the minimum of DTG curves (Tmax)

corresponds to the maximum weight loss at that particular

temperature.

It can be seen from the TG and DTG curves that the delay

in the onset of loss temperature in the plasticizers loss zone

(Tmax between 150 and 250 8C) is higher in case of EG and PG

plasticized resin compared to glycerol plasticized material.

A broad weight loss step in the plasticizer loss zone can

clearly be seen in glycerol plasticized resin, potentially due

to glycerol which is loosely bound with protein (glycerol-

rich zone) and glycerol which is more strongly bonded with

protein. Similar degradation patterns were observed while

studying degradation behavior of glycerol plasticized

cottonseed proteins.[3] On the other hand, the relatively

higher stability of DET plasticized resins compared to other

plasticized materials may result from the comparatively

high molecular mass of the DET. DET also has the lowest

ability to plasticize and break protein/protein interactions.

fiber 12.28

EG plasticized 8.36

PG plasticized 7.92

G plasticized 19

DET plasticized 5.48

3.6. Water Uptake Studies

In WU experiments, the mass of sorbed moisture is

measured as a function of time. The WU during exposure

to 98% RH of the fiber and plasticized resins versus time was




evaluated. The WU curves of the fiber and plasticized resins

are shown in Figure 9. It was observed that all specimens

absorbed water during the experiment. The diffusion of

water is remarkably influenced by the microstructure of the

polymeric materials, and type, and mass of the plasticizers

as well as water affinity of the components.[43] There are

two well-separated zones for all the curves as displayed in

Figure 9. As reported previously in plasticized soy protein

and starch systems,[4,44] the kinetics of absorption was fast

at lower times, whereas at longer conditioning times the

kinetics of absorption became slow. The maximum relative

WU, or WU at equilibrium corresponding to plateau values

are presented in Table 3. The highest WU in the presence of

glycerol suggests that the affinity between glycerol and

water is higher than even fiber keratin and water.

This pronounced rate of WU may be due to the presence

of loose glycerol-rich domains as evidenced by DMA and

DSC characterization. Similarly Chen et al.[20] evidenced

higher WU by glycerol plasticized SPI due to the presence of

glycerol rich domains especially when glycerol concentra-

tion was more than 25 wt% of SPI. The lower moisture

uptake of EG plasticized material compared to neat fiber

: 10.1002/mame.201200010



Figure 10. (A) Dependence of optical transmittance (%) of extruded resins on the type of plasticizer used at different wavelengths and (B)digital photographs of their corresponding 1 mm thick specimens.


www.mme-journal.de

and glycerol plasticized fiber can be explained due to the

stronger hydrogen bonding between fiber keratin and EG

and water adsorption capacity of EG-fiber keratin networks

is lower than fiber keratin and glycerol plasticized resins.

The least WU by PG, and DET plasticized samples might be

due to more hydrophobic nature and higher molecular mass

of these plasticizers compared to EG.

The opacity or transparency of materials can also be used

as an auxiliary criterion to judge the compatibility and

homogeneity of blends.[45] Figure 10A shows the depen-

dence of percent optical transmittance at different

wavelengths on type of plasticizer used. The transmittance

values of the plasticized resins in the visible region (400–

800 nm) are in the order of DET plasticized<G plastici-

zed< PG plasticized< EG plasticized resin. Interestingly,

the EG plasticized film was the most transparent among all

which was also confirmed by the visual inspection of the

samples (Figure 10B). The relatively darker appearance of

glycerol plasticized film may be due to the degradation of

keratin in protein-rich zones during thermal processing.

4. Conclusion

Feather fiber keratin can be processed into thermoplastics

of different transparencies and physical properties by

extrusion processing with the addition of different

plasticizers. The fixed concentration of plasticizers

(30 wt%, dry basis of fiber) was used. Among the various

plasticizers investigated, PEG, sorbitol, and lactic acid were

found to be ineffective to plasticize fiber keratin. Suitable

materials were obtained in the presence of EG, PG, glycerol,

and DET as plasticizers. The highest compatibility and

strongest H-bonding was seen for EG, while glycerol had

complex interactions with the fiber keratin. Relatively low





H-bonding occurred between the fiber keratin and PG and

the lowest with DET. Both PG and DET transformed fiber

into relatively hard and brittle bioplastic compared to EG

and glycerol. All plasticizers were able to plasticize fiber

keratin; however, the best mechanical properties, transpar-

ency, flowability, and processability were seen with the

addition of EG. Addition of all plasticizers increased water

resistance of fiber keratin except glycerol. The glycerol

plasticized material appears as a complex heterogeneous

system composed of glycerol-rich and protein-rich

domains.

Acknowledgements: The authors gratefully acknowledge thefinancial support for current work from Alberta Innovates –Biosolution Corporation and the Biorefining Conversions Network.The authors also acknowledge Prof. Thava Vasanthan andDr. Anastasia Elias for providing extruder and DMA facilitiesand helpful discussions.

Received: January 12, 2012; Published online: DOI: 10.1002/mame.201200010

Keywords: extrusion; fiber keratin; plasticizers; thermoplastics;water resistance

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Feather Fiber-Based Thermoplastics: Effects of Different Plasticizers on Material Properties