- Email: [email protected]
Preparation and characterisation of mechanically milled particles from waste alpaca fibres
Accepted Manuscript Preparation and characterisation of mechanically milled particles from waste alpaca fibres
Md Abdullah Al Faruque, Rechana Remadevi, Xungai Wang, Maryam Naebe PII: DOI: Reference:
S0032-5910(18)30892-1 doi:10.1016/j.powtec.2018.10.049 PTEC 13824
To appear in:
Powder Technology
Received date: Revised date: Accepted date:
31 August 2018 21 October 2018 23 October 2018
Please cite this article as: Md Abdullah Al Faruque, Rechana Remadevi, Xungai Wang, Maryam Naebe , Preparation and characterisation of mechanically milled particles from waste alpaca fibres. Ptec (2018), doi:10.1016/j.powtec.2018.10.049
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Preparation and characterisation of mechanically milled particles from waste alpaca fibres Md Abdullah Al Faruque, Rechana Remadevi, Xungai Wang and Maryam Naebe* Deakin University, Institute for Frontier Materials (IFM), Geelong, Victoria 3216, Australia
AC
CE
PT E
D
MA
NU
SC
RI
PT
*corresponding author`s email: [email protected]
ACCEPTED MANUSCRIPT Abstract In this work, a chemical free green processing route was followed to fabricate alpaca powders from waste alpaca fibres. The waste fibres were converted into powders with the average particle size of 2.5 μm without using any chemicals neither in pre-treatment nor in powder fabrication process. Despite visible morphological changes of the powder samples, Nuclear
PT
Magnetic Resonance Spectroscopy (NMR) and Fourier Transform Infrared (FTIR) revealed
RI
no chemical change or shift in the functional groups. The crystallinity of the powdered
SC
samples decreased with the reduction of particle size in different stages of the milling process. The differential scanning calorimetry (DSC) and thermogravimetric (TGA) test
NU
results revealed that the thermal stability of the alpaca powder was almost similar to that of alpaca fibre. The air jet-milled powder showed an increase in moisture regain and moisture
MA
content by around 38% and 33% respectively than that of alpaca fibres. The results suggest that alpaca powders have a great potential to be introduced to a wide range of new
PT E
D
applications.
Keywords: Protein fibre; mechanical milling; particle size; characterisation; NMR,
AC
CE
moisture properties.
ACCEPTED MANUSCRIPT
1. Introduction Keratinous and non-keratinous protein fibres are widely used in textiles due to their high quality and accessibility [1]. The waste fibres produced from these sources are enormous. A practical way of breaking down these waste materials is converting the waste fibres into fine
PT
powders to be used in coating, drug delivery, cosmetics, environmental protection, composite
RI
films and fibres preparation [2]. For example, while a very unique way of converting wool
SC
fibres into nano-scale particles was reported, the particles were used as a film on the surface of pure cotton fabric that resulted in changing the functional properties of the fabric [3]. The
NU
cotton fabric coated with the particles showed lower moisture absorbency and increased the thermal retention property compared with uncoated fabric [3]. Wool powder blended
MA
polypropylene fibres were produced with the fineness of around 3 dtex/filament, where by incorporating 2-3% of wool particles, the blended fibres showed greater elastic recovery,
D
moisture and dye-uptake properties than the pure polypropelene fibres [4]. In another work,
PT E
wool fibres were converted into powders by using the air jet-milling technique and the dye/metal ion (Co2+, Cu2+ and Cd2+) absorption capability of the wool powders was studied
CE
[5]. It was found that the moisture absorption of the powdered wool samples reduced while
AC
the dye/metal ion absorption ability of the wool particles increased [5]. It has been reported that pulverized chicken feather particles can act as a bio-sorbent of precious metals (e.g. gold and platinum), capable of controlling water pollution [6] and silk particles have the potential for use in drug delivery and in the cosmetic industry [7]. Moreover, wet milled powder particles, fabricated from cashmere guard hair, were used for the absorption of metal ions (e.g. Zn2+ and Cr6+ ) from the aqueous solution. The cashmere powders were more efficient in absorbing Cr6+ compared with wool and silk powders due to the higher disruption in cuticle cells of guard hair and the higher oxidation of the cashmere powder surface [8].
ACCEPTED MANUSCRIPT The animal protein fibres can be converted into fine powder particles using two different approaches, namely, the chemical or bottom-up approach and the mechanical or top-down approach [9]. In the bottom-up approach, the fibres are dissolved in a suitable solvent that disrupts the intermolecular bonds and solubilizes the fibres and finally, the solution is converted into the fine particles [9]. However, in this method toxic chemicals are often
PT
required to be used which can diminish the natural properties of the fibres and are harmful to
RI
the environment. Moreover, this method is costly and time-consuming [10]. Another
SC
approach, known as the top-down approach, is the mechanical milling process where the natural fibres, like cotton, wool, silk and cashmere or the metal and ceramics, for example,
NU
aluminium (Al) and boron carbide (B4C) are first chopped into small particles. And then by applying different milling techniques like planetary ball milling [11, 12] and wet attritor
MA
milling [13] are ground into fine particles. In this method, the powders can retain or improve the inherent characteristics (e.g. biodegradability, biocompatibility, moisture and dye uptake
D
properties) of fibres [3, 6-8, 13]. Between the two approaches, the top-down approach of
PT E
powder formation is easy, safe, quick and environmentally friendly [9, 12]. Alpaca is a keratinous protein fibre similar to wool, cashmere and other hair fibres in its
CE
physical and chemical characteristics. In addition, it is a special and luxurious fibre with
AC
excellent softness, great warmth, good lustre and strength [14, 15]. Moreover, inherently alpaca fibres come in 22 shades of colour as reported by Fan et al. [16]. It is reported that annually 5000 tonnes of alpaca fibres are produced worldwide.
During shearing and
processing the alpaca fibres, around 20-30% of short and non-spinnable fibres are produced, mostly ending in landfill, fed into incinerator or used as low-grade animal feed [17-19]. Although the converted waste alpaca fibres into fine powder particles may have high potential to be used in different areas, there is no report on powder formation of alpaca fibre. Moreover, as alpaca fibre comes with different shades of colour, the fine alpaca particles
ACCEPTED MANUSCRIPT could also be used as a colour pigment that has not been addressed in literature. In this study and for the first time, waste alpaca fibres were successfully converted into fine powder particles by following the mechanical milling process. Previously different chemical pretreatment techniques were adopted to ease the powder formation process of other protein fibres like cashmere and wool [20, 21]. However, in the current study, no chemical pre-
PT
treatment was implemented neither to accelerate the mechanical milling process nor to reduce
RI
the particle size. A detailed characterisation of the fabricated powder materials from protein
SC
fibres is missing in literature, hindering the proper understanding of potential application areas of the developed protein powders from fibres. Therefore, in this study, the produced
NU
powders from waste alpaca fibres were characterised by their particle size distribution, morphological, structural, thermal and moisture uptake properties to better understand the
MA
newly formed powder materials.
PT E
2.1. Materials preparation
D
2. Materials and methods
Black waste alpaca fibres were supplied by Nocturne Alpacas, Buckley, VIC 3240, Australia.
CE
The mean staple length and diameter of the used alpaca fibre were 65.58 mm and 21 μm, respectively. After removing different impurities such as vegetable matters, the fibres were
AC
washed with commercially available Eucalyptus wool wash as the detergent. Finally, the fibres were rinsed with water and dried in a conventional oven overnight at 60⁰C. 2.2. Powder fabrication The powder fabrication process was carried out by following the method previously explained [13]. Briefly, the dried alpaca fibres were chopped with a rotary cutter mill (Pulverisette 19 from Fritsch GmbH, Germany) to make snippets of approximately 1 mm in length. The snippets were then milled with an Attritor mill (2S, Union Process, USA) to
ACCEPTED MANUSCRIPT produce alpaca slurry. The attritor mill was equipped with a drum containing ceramic balls, an agitator shaft, and sets of impeller (inside of the drum). These impellers were set at right angle to each other, capable of producing higher energy to convert the particles into lowered particle size. Alpaca snippets (200 g) were mixed with 2 litre of deionised (DI) water and fed into the grinding chamber of the attritor mill. During the milling process, the agitator was
PT
kept running at 280 rpm for 6 hrs to convert the snippets into a slurry. After slurry formation,
RI
it was dried by using a laboratory scale mini spray dryer (B-290, Buchi Labortechnik AG,
SC
Switzerland) producing the spray dried powder. The slurry flowed into the dryer at 10 ml/min with the inlet air temperature of 180⁰C and the outlet air temperature of 100⁰C. The spray
NU
dried powders were then passed through the air jet milling process using the laboratory air jet mill (Sturtevant Inc, USA) at 110 PSI grinding air pressure. Digital images of the alpaca fibre
MA
(AF), alpaca snippets (AS), attritor milled slurry (AMS), spray dried powder (SDP) and air jet-milled powder (AJM) samples are shown in Fig. 1. The instruments used in the powder
PT E
D
fabrication method are presented in Fig. 2.
and d) air jet mill.
AC
CE
Fig. 1. Instruments used in powder fabrication: a) cutter mill, b) attritor mill, c) spray dryer
Fig. 2. Digital images of samples: a) alpaca fibres (AF), b) alpaca snippets (AS), c) attritor milled slurry (AMS), d) spray dried powder (SDP) and e) air jet milled powder (AJM).
2.3. Particle size measurement
ACCEPTED MANUSCRIPT The particle size of the alpaca snippets, slurry, spray dried powder and air jet-milled powder was measured by using the Malvern mastersizer 2000, USA fitted with Hydro 2000S. The refractive index of alpaca fibre (1.56) was used during the measurement. Alpaca powders were dispersed in DI water and then added to the mastersizer for particle size measurement. The data was collected after each sample was measured four times. The volume-based
PT
particle size method was adopted to analyse the results, where the volume median diameter
RI
d(0.5) represents that 50% of particles are above and 50% below the stated size. In addition,
SC
d(0.1) and d(0.9) values denote that 10% and 90% of the measured particles were less than the presented size [22]. Error bars were not considered due to insignificant variation in d(0.5)
MA
2.4. Scanning Electron Microscopy (SEM)
NU
measurements per powder sample from the Mastersizer 2000.
The morphologies of alpaca fibres and powders were analysed by using a Zeiss Supra 55VP
D
scanning electron microscope (SEM) at an accelerating voltage of 3 kV. Prior to the imaging,
PT E
all the samples were gold coated using Leica EM ACE600 gold coater. 2.5. Fourier Transform Infrared (FTIR)
CE
The Fourier transform infrared (FTIR) spectra of alpaca fibre and its powder samples were performed under Attenuated Total Reflectance (ATR) mode using Vertex 70 (Bruker,
AC
Germany) spectrometer with a scan resolution of 4 cm-1 and 32 scans per sample between 400 cm-1 and 4000 cm-1. The data was subjected to baseline correction by OPUS software 5.5. 2.6. X-ray diffraction (XRD) The effect of the powder formation process on the crystallinity of the alpaca fibres was analyzed by X-ray diffraction (XRD) technique (X’Pert Powder, PANalytical, Netherlands), at 40 kV operating voltage and current flow of 30 mA. The measurement was taken between
ACCEPTED MANUSCRIPT 6 degrees and 40 degrees; step size was 0.013⁰ and 250s per step. The crystallinity index (Cr.I.) of the parent fibres and the powders was calculated by Equation (1) [23]: Cr.I. = (I9 - I14) * 100 / I9
(1)
where Cr.I. is the crystallinity index, I9 is the maximum intensity in arbitrary units with 2-
PT
theta at 9⁰ and I14 is the maximum intensity in arbitrary units with 2-theta at 14⁰. In general,
SC
2.7. Nuclear Magnetic Resonance Spectroscopy (NMR)
RI
the higher Cr.I. value represents the higher crystallinity of the sample [24].
solid-state
13
NU
The 1H NMR and 13C NMR spectra were recorded on a Bruker spectrometer, Germany. The C CP-MAS NMR spectra of the samples were recorded on a 300 MHz Bruker
MA
Ascend 300 WB spectrometer by using a 4 mm rotor at 10 KHz spinning rate and 1600 scans for each sample. All the data were extracted using TopSpin 3.2 software.
PT E
D
2.8. Differential Scanning Calorimetry (DSC) Differential Scanning Calorimetry (DSC) test was carried out by DSC Q200 (TA Instruments, USA). The samples (5 mg) were heated from ambient temperature to 300⁰C at a
CE
heating rate of 10⁰C/min in a nitrogen atmosphere.
AC
2.9. Thermogravimetric analysis (TGA) Thermogravimetric analysis (TGA) was carried out by using TGA Q50 (TA Instruments, USA), where the samples (5 mg) were heated from room temperature to 600⁰C at a heating rate of 10⁰C/min in a nitrogen atmosphere. 2.10. Moisture properties The percentage of moisture regain (MR) and moisture content (MC) of the alpaca fibres, snippets, spray dried and air jet-milled powders were measured by the ASTM D1576-13
ACCEPTED MANUSCRIPT method illustrated in the literature [25, 26]. Briefly, approximately 2 g of each sample was conditioned at 20⁰C±2⁰C and 62%± 2% RH (relative humidity) for 2 days. The conditioned samples were then weighed and dried at 110⁰C for 4 hours in an oven. The samples were reweighed and moisture regain and content were calculated from Equation (2) and Equation
PT
(3), respectively:
MC (%) = (M-D) / M * 100
RI
MR (%) = (M-D) / D * 100
(2) (3)
SC
where M is the weight of the conditioned sample and D is the weight of the oven-dried
NU
sample. Each sample was tested five times and the result was reported as an average.
MA
3. Results and discussion 3.1. Particle size of the samples
D
The volume-based particle size distribution of the alpaca samples after each step of powder
PT E
formation is shown in Fig. 3. Table 1 shows the particle size values of d(0.1), d(0.5) and d(0.9) at different phases of powder fabrication. It is evident that during snippets and attritor
CE
milled slurry formation the particle size of the fibres reduces. The reduction in particle size of d (0.5) from 70.04 μm to only 2.88 μm during attritor milling can be due to the combined
AC
action of the impellers and ceramic balls inside the milling drum. During the rotation of the agitator shaft inside the drum, the snippets passed through continuous and vigorous beating that reduced the alpaca particle size in the slurry. In contrast, after the spray drying process the particle size of d(0.5) increased to7 μm. This may be due to the particle aggregations at the time of spray drying or loss of finer particles as the slurry passes through the nozzle and the cyclone of the spray dryer [13]. However, it could be possible to break-down the aggregated particles further into a smaller size by using the air jet-milling process. During air
ACCEPTED MANUSCRIPT jet milling, the spray dried powders are fed into an air vessel by a feed plate to further decrease the particle size. The compressed grinding air pressure fed into the chamber creates an air vortex due to high speed which reduces the particle size of d(0.5) to 2.5 μm. It has been reported that the particle size of pigments that can be used as textile colourant, ranges between 1-75 μm [27]. While alpaca fibres are naturally coloured fibres in 22 different colour
PT
shades [16], our group has shown that both the spray dried (7 μm) and air jet-milled (2.5 μm)
RI
powders have high potential to be used as pigments for colouration of regenerated fibres
SC
(unpublished results).
Table 1 The particle size of alpaca powders at different stages of powder formation
Alpaca snippets
20.56
Attritor milled slurry
1.31
Spray dried powder
2.80
Air jet-milled powder
1.10
d (0.5) (μm)
d (0.9) (μm)
70.04
580.45
NU
d (0.1) (μm)
2.88
6.68
7.14
16.63
2.55
6.89
CE
PT E
D
MA
Sample name
Fig. 3. Particle size distribution of alpaca fibre at different stages of mechanical milling;
AC
snippets (AS), slurry (AMS), spray dried powder (SDP) and air jet milled powder (AJM).
3.2. Morphology of alpaca fibre and powders The morphology of alpaca fibre and its powders at different stages of powder formation is shown in Fig. 4. The SEM image of Fig. 4 (a) shows overlapping cuticle scales on the surface of the alpaca fibre similar to wool and other hair fibres [28]. It is observed that when alpaca
ACCEPTED MANUSCRIPT fibres were split by cutter mill into snippets, the scales of the parent fibre were retained without complete destruction of the cuticle as shown in Fig. 4 (b). The spray dried powders look like agglomerated particles in Fig. 4 (c). However, after the air jet milling process the particles were converted into smaller particle size as shown by particle size analysis (Table 1) and Fig. 4 (d). From the SEM images, it is evident that the cuticle, cortex, and microfibrils of
PT
the parent alpaca fibres are significantly destroyed in both the spray dried and air jet-milled
RI
powders. This is due to the extensive wet attritor milling process and also the consecutive
SC
drying processes [13, 20]. While observation of the morphology of alpaca fibres assists in understanding the effect of mechanical milling on powder, the loss in the inner and outer
MA
powders, which will be discussed later.
NU
structure of the fibres can affect the crystallinity and moisture absorbing properties of the
3.3. FTIR analysis
powder.
PT E
D
Fig. 4. SEM images: a) Alpaca fibre, b) snippets, c) spray dried powder and d) air jet-milled
CE
The FTIR analysis of alpaca fibre and its powders produced at different steps is presented in
AC
Fig. 5. The FTIR spectra of powders revealed similar peak positions to the alpaca fibres. No new peaks or peak shifting were found in the functional groups of the powder samples. The region between 1300 cm-1 and 1700 cm-1 represents the protein amide group where peaks at 1450-1500 cm-1 correspond to methyl C-H deformation. In addition, the peak position between 1600 cm-1 and 1700 cm-1 region represents protein amide I of C=H stretching [29]. In general, the peaks at 1648-1660 cm-1, 1540-1550 cm-1, 1235-1250 cm-1 and 3300 cm-1 represent the amide I, amide II, amide III and amide A (N-H stretching) regions of the protein structure, respectively [30]. Another two prominent peaks are 2850 cm-1 and 2930 cm-1
ACCEPTED MANUSCRIPT representing the symmetric and asymmetric C-H stretching vibrations of methylene [31]. In this study, the powder fabrication method was performed by a mechanical milling process without adding any chemicals. Therefore, it can be concluded that the mechanical milling process had no adverse effect on the functional groups of the alpaca fibres.
RI
and air jet-milled powder (AJM).
PT
Fig. 5. FTIR analysis of alpaca fibre (AF), alpaca snippets (AS), spray dried powder (SDP)
SC
3.4. XRD analysis
NU
The diffraction patterns of alpaca fibres and powders are shown in Fig. 6. The crystallinity index values (Cr.I.) of the fibres and powders are also shown in Table 2. The diffraction
MA
pattern of alpaca fibre shows a minor 2θ peak at 9⁰ of crystalline spacing of 9.8 Å and a strong 2θ peak at 20⁰ indicating the crystalline spacing of 4.4 Å [28]. It is well known that the
D
peak at 2θ 9⁰ refers to the α-helix structure while the peak at 2θ 20⁰ corresponds to the β-
PT E
sheet configuration [32]. When the fibres are converted into powders by the mechanical process, the intensity of the minor 2θ peak at 9⁰ gradually reduces and the 2θ peak of 20⁰
CE
becomes broader in range compared to the peak representing the parent alpaca fibre. This steady deterioration and broadening of peaks represent the increase in disoriented areas in the
AC
β-sheet configuration that leads to the lower crystalline structure in smaller particle size samples [12, 33]. Previously, it has been reported that the cuticle which is the outermost layer in protein fibres, possesses the most regular crystalline structure [34]. However, due to attritor milling and subsequent drying processes during powder formation, the outermost layers of the alpaca fibres were completely destroyed in both spray dried and air-jet milled powder. This deterioration in layers maybe accountable for the lower crystalline (Table 2) and subsequent higher amorphous structures in alpaca powders than that of parent fibres [12].
ACCEPTED MANUSCRIPT The higher amorphous region of the powders can be useful where higher moisture properties are required for new applications (e.g pigments). Table 2 Crystallinity index values of alpaca fibres and powders
Crystallinity index (%)
Alpaca fibre (AF)
42.95
Alpaca snippets (AS)
33.18
Spray dried powder (SDP)
29.58
Air jet-milled powder (AJM)
27.03
MA
NU
SC
RI
PT
Sample name
Fig. 6. XRD analysis of alpaca fibre (AF), alpaca snippets (AS), spray dried powder (SDP)
PT E
D
and air jet-milled powder (AJM).
CE
3.5. NMR spectroscopy analysis
The fine structures of alpaca fibres and its powder materials were investigated by solid-state 13
AC
C CP MAS NMR as shown in Fig. 7. The different spectra in Fig. 7 show the typical
asymmetric peak in between 170 and 174 ppm that represents the carbonyl (C=O) group of keratinous material [35, 36]. The peak at 130 ppm refers to various aromatic carbons (C=C) existing in keratin [36]. From Fig. 7, it was also found that all the powder samples retained this similar peak position at 130 ppm, which suggests no disruptions to aromatic regions of the protein fibres while converting to powders through the mechanical milling process. The other two peaks at 55 ppm and 40 ppm represent the α-carbons and β-carbons, respectively.
ACCEPTED MANUSCRIPT The peaks between 25 ppm and 35 ppm are attributed to the alkyl groups of the side chains [36]. It has been reported that β-carbons are mainly present in leucine and cysteine residues and the peaks between 25 ppm and 35 ppm represent carbons in glutamine, proline and glutamic acid residues [37]. From the NMR spectroscopy, it is confirmed that like other keratinous materials, alpaca possesses similar carbon peaks. Consistent with the findings
PT
from FTIR and XRD, NMR results further confirmed neither new chemical bond formation
SC
RI
nor peak shifting occurred in the mechanically milled alpaca powder.
NU
Fig. 7. 13C NMR spectra of alpaca fibre (AF), alpaca snippets (AS), spray dried powder
MA
(SDP) and air jet-milled powder (AJM).
D
3.6. DSC analysis
PT E
The differential scanning calorimetric plots of the samples are shown in Fig. 8. Three thermal events are described by the DSC test such as glass transition, moisture evaporation and
CE
denaturation [38]. The glass transition of the alpaca fibres and powders ranges between 40⁰C
AC
and 60⁰C [38]. From Fig. 8, it is evident that the glass transition temperature of alpaca fibre and snippets is almost identical. On the other hand, spray dried powder shows the highest glass transition temperature and in the case of air jet-milled powder, it is the lowest. This might be due to the agglomeration of the particles. As explained before, during spray drying due to loss of fine particles or agglomeration, the particle size increased in spray dried powders that is further reduced by air jet milling [13]. Therefore, as the particles are more agglomerated in spray dried powders, these are showing higher Tg than others. In addition, the breaking of the agglomerated particles reducing the
particle size, glass transition
ACCEPTED MANUSCRIPT temperature decreased in the air jet milled powder [39]. Similarly, due to the lower particle size and reduced crystallinity, the water evaporation temperature of the air jet-milled powder increases compared to the other samples [38]. The other major peak between 230⁰C and
PT
240⁰C is attributed to crystal disruption of the α-keratinous materials of the fibres [38, 40].
Fig. 8. DSC analysis of alpaca fibre (AF), alpaca snippets (AS), spray dried powder (SDP)
SC
RI
and air jet milled powder (AJM).
NU
3.7. TGA analysis
MA
The thermogravimetric analysis (TGA) of alpaca fibres, snippets, spray dried and air jetmilled powders are shown in Fig. 9. It is evident that the main weight loss took place at temperature ranges from 30⁰C to 120⁰C and 220⁰C to 450⁰C, respectively. The first weight
PT E
D
loss is attributed to the loss of moisture [1]. Generally, because of reduced particle size, the crystalline region is destroyed and amorphous region is increased that promotes a higher moisture absorbing property [1]. It is worth mentioning that the total water evaporation range
CE
between 120⁰C and 150⁰C for very small powdered particles has also been reported [41]. In
AC
this study, the TGA curve can be divided into two stages; one is between 30⁰C and 120⁰C that can be attributed to the loss of water and another one is between 220⁰C and 450⁰C that could be due to the destruction of intermediate protein molecules like hydrogen sulphide and sulphur dioxide [1]. Although the alpaca snippets and air jet-milled powders are showing almost similar thermal behaviour to the parent fibre, the spray dried powder is presenting slightly higher thermal behaviour. As discussed by DSC results, this is also due to the agglomeration of particles in the spray dried powders while fabricating the powders from the fibres. In addition, as the maximum thermal decomposition temperatures of the snippets,
ACCEPTED MANUSCRIPT spray dried powders and air jet-milled powders are not lower than that of parent fibres (Fig. 9), it can be concluded that the thermal stability of the powder particles produced by mechanical milling has not been degraded [1]. Currently, our group is working on fabrication of composite fibres from alpaca powder and polyacrylonitrile (PAN) and it has been found that the thermal stability of the composite fibres enhanced due to higher thermal properties of
PT
the alpaca compared to the PAN (unpublished result). However, previously it was reported
RI
that when wool fibre was converted into powder by using a chemical process, the thermal
SC
stability of the powder deteriorated [10].
NU
Fig. 9. TGA analysis of alpaca fibre (AF), alpaca snippets (AS), spray dried powder (SDP)
MA
and air jet-milled powder (AJM).
PT E
D
3.8. Moisture properties of the alpaca samples The moisture regain (MR) and moisture content (MC) of alpaca fibres, snippets, spray dried powders and air jet-milled powders are shown in Fig. 10. It is observed that with the
CE
reduction in particle size the moisture uptake (%) gradually increases among the powder
AC
samples. This might be due to the reduction in the crystalline region as explained before, thereby enhancing the amorphous region to facilitate penetration of water molecules into the powders that eventually improves the moisture absorbing capacity of the powders. In addition, reduction in the particle size leads to increased surface areas; with the increase in surface area, the number of water molecules peneterating into the powders increases. Similar results were found when wool fibres were converted into fine powders, the particle size reduced and affinity towards water increased [28]. In this study, the air jet-milled powder shows a higher moisture regain (20.13%) and moisture content (16.59%) than the other
ACCEPTED MANUSCRIPT powders and alpaca fibres. Therefore, as the powder exhibited enchanced moisture properties, based on the final application and as required seems that it can be applied to any synthetic polymer to enhance the moisture properties.However, an exception was found while the wool fibres were converted into powders for dye and metal ion sorption [5]. The author reported lower moisture absorption properties because of higher cystallinity of the powders, although
PT
the crystallinity index was not calculated. In addition, from the author’s X-ray photoelectron
RI
spectroscopy (XPS) analysis, it was found that with the reduction in particle size, the carbon
SC
(C) content was decreased from around 78% to 66% and oxygen (O) content was increased from approximately 11% to 18% that ensures the high water absorption tendency of the wool
NU
powders. Moreover, the author also mentioned that during the milling process the cuticle cells of the fibres were destroyed and the cortex of the fibres exposed which may also be
MA
responsible for the higher moisture absorption. It is not completely clear why this
PT E
D
phenomenon was reported.
Fig. 10. Moisture regain (%) and moisture content (%) of alpaca fibre (AF), alpaca snippets
AC
4. Conclusion
CE
(AS), spray dried powder (SDP) and air jet-milled powder (AJM).
In this study, the waste alpaca fibres were converted into powders by the mechanical milling process without any chemical pre-treatment. It was found that the particle size of the fibres was gradually reduced at every step of the milling process although it increased during the spray drying process due to agglomeration of the particles. While the morphological analysis confirmed that mechanical milling is capable of producing the fine powder particles from the fibres, the smallest particle size of 2.5 µm was found after the air jet-milling. Chemical
ACCEPTED MANUSCRIPT analysis revealed no chemical changes or peak shifting in functional groups of the powder compared to the alpaca fibres. As a result, it is expected that the inherent properties of the fibres is retained. However, the crystallinity of the powders reduced gradually due to the lower particle size. Thermal analysis further confirmed that the thermal stability of the powder particles did not deteriorate compared to the parent fibre. The alpaca powders showed
PT
an increase in moisture properties over that of the parent fibres. These findings will help the
RI
possible development of certain application areas of alpaca powders, such as fabricating
SC
pigments for colouration, or manufacturing composite films or fibres with enhanced moisture and thermal properties.
NU
Acknowledgement
MA
The current study was supported by Deakin University Postgraduate Research Scholarship (DUPRS) awarded to the first author, and was carried out with the support of the Deakin
AC
CE
PT E
D
Advanced Characterization Facility.
ACCEPTED MANUSCRIPT References
AC
CE
PT E
D
MA
NU
SC
RI
PT
[1] W. Xu, W. Guo, W. Li, Thermal analysis of ultrafine wool powder, Journal of Applied Polymer Science, 87 (2003) 2372-2376. [2] K. Patil, R. Rajkhowa, X. Wang, T. Lin, Review on fabrication and applications of ultrafine particles from animal protein fibres, Fibers and Polymers, 15 (2014) 187. [3] J. Hu, Y. Li, Y. Chang, K. Yeung, C. Yuen, Transport properties of fabrics treated with nano-wool fibrous materials, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 300 (2007) 136139. [4] G. Xushan, Development of wool powder/polypropylene blend fibers, Melliand International, 12 (2006) 267. [5] G. Wen, Characterization and sorption ability of wool powder, Institute for Frontier Materials, Deakin University, Geelong, Victoria, Australia, 2009, pp. 1-134. [6] K. Suyama, Y. Fukazawa, H. Suzumura, Biosorption of precious metal ions by chicken feather, Applied Biochemistry and Biotechnology, 57 (1996) 67. [7] T. Une, K. Kusaki, T. Hiroyuki, Properties of silk pigments and its use for cosmetics, Fragrance Journal, 4 (2000) 15-21. [8] K. Patil, S.V. Smith, R. Rajkhowa, T. Tsuzuki, X. Wang, T. Lin, Milled cashmere guard hair powders: Absorption properties to heavy metal ions, Powder Technology, 218 (2012) 162-168. [9] M. Kazemimostaghim, R. Rajkhowa, X. Wang, Comparison of milling and solution approach for production of silk particles, Powder Technology, 262 (2014) 156-161. [10] K. Wang, R. Li, J. Ma, Y. Jian, J. Che, Extracting keratin from wool by using L-cysteine, Green Chemistry, 18 (2016) 476-481. [11] A. Canakci, T. Varol, F. Erdemir, S. Ozkaya, New Coating Technique for Al–B 4 C Composite Coatings by Mechanical Milling and Composite Coating, Powder Metallurgy and Metal Ceramics, 53 (2015) 672-679. [12] F. Erdemir, Study on particle size and X-ray peak area ratios in high energy ball milling and optimization of the milling parameters using response surface method, Measurement, 112 (2017) 53-60. [13] R. Rajkhowa, Q. Zhou, T. Tsuzuki, D.A. Morton, X. Wang, Ultrafine wool powders and their bulk properties, Powder Technology, 224 (2012) 183-188. [14] X. Wang, L. Wang, X. Liu, The quality and processing performance of alpaca fibres: A report for the rural industries research and development corporation, RIRDC Publication, (2003). [15] C. Lupton, A. McColl, R. Stobart, Fiber characteristics of the Huacaya Alpaca, Small Ruminant Research, 64 (2006) 211-224. [16] R. Fan, G. Yang, C. Dong, Study of hair melanins in various hair color Alpaca (Lama Pacos), AsianAustralasian Journal of Animal Sciences, 23 (2010) 444-449. [17] A. Shavandi, T.H. Silva, A.A. Bekhit, A.E.-D. Bekhit, Dissolution, Extraction and Biomedical Application of Keratin: Methods and Factors Affecting the Extraction and Physicochemical Properties of Keratin, Biomaterials Science, (2017). [18] Y. Zhang, R. Yang, W. Zhao, Improving digestibility of feather meal by steam flash explosion, Journal of Agricultural and Food Chemistry, 62 (2014) 2745-2751. [19] S. Huda, Y. Yang, Feather fiber reinforced light-weight composites with good acoustic properties, Journal of Polymers and the Environment, 17 (2009) 131. [20] K. Patil, R. Rajkhowa, X.J. Dai, T. Tsuzuki, T. Lin, X. Wang, Preparation and surface properties of cashmere guard hair powders, Powder Technology, 219 (2012) 179-185. [21] Y. Cheng, C. Yuen, Y. Li, S. Ku, C. Kan, J. Hu, Characterization of nanoscale wool particles, Journal of Applied Polymer Science, 104 (2007) 803-808. [22] G. Niro, GEA Niro Method No, A, 2005. [23] S. Zheng, Y. Nie, S. Zhang, X. Zhang, L. Wang, Highly efficient dissolution of wool keratin by dimethylphosphate ionic liquids, ACS Sustainable Chemistry & Engineering, 3 (2015) 2925-2932.
ACCEPTED MANUSCRIPT
AC
CE
PT E
D
MA
NU
SC
RI
PT
[24] H. Xu, Y. Yang, Controlled de-cross-linking and disentanglement of feather keratin for fiber preparation via a novel process, ACS Sustainable Chemistry & Engineering, 2 (2014) 1404-1410. [25] R. Remadevi, S. Gordon, X. Wang, R. Rajkhowa, Investigation of the swelling of cotton fibers using aqueous glycine solutions, Textile Research Journal, 87 (2017) 2204-2213. [26] A.S.T.M., Standard Test Method for Moisture in Wool by Oven-Drying, D1576-13, ASTM International, West Conshohocken, PA, 2013. [27] A.M. Gueli, G. Bonfiglio, S. Pasquale, S.O. Troja, Effect of particle size on pigments colour, Color Research & Application, 42 (2017) 236-243. [28] W. Xu, W. Cui, W. Li, W. Guo, Development and characterizations of super-fine wool powder, Powder Technology, 140 (2004) 136-140. [29] R. Li, D. Wang, Preparation of regenerated wool keratin films from wool keratin–ionic liquid solutions, Journal of Applied Polymer Science, 127 (2013) 2648-2653. [30] A. Aluigi, M. Zoccola, C. Vineis, C. Tonin, F. Ferrero, M. Canetti, Study on the structure and properties of wool keratin regenerated from formic acid, International Journal of Biological Macromolecules, 41 (2007) 266-273. [31] J.-H. Hsu, S.-L. Lo, Chemical and spectroscopic analysis of organic matter transformations during composting of pig manure, Environmental Pollution, 104 (1999) 189-196. [32] E. Bendit, A quantitative x-ray diffraction study of the alpha-beta transformation in wool keratin, Textile Research Journal, 30 (1960) 547-555. [33] G. Jeffrey, J. Sikorski, H. Woods, The Mechanism of Supercontraction in Keratin, Textile Research Journal, 25 (1955) 714-722. [34] I. Fouda, M. El-Tonsy, H. Hosny, Effect of the oxidative power of iodination on the optical properties of Alpaca fibres, Polymer Degradation and Stability, 46 (1994) 287-294. [35] A. Idris, R. Vijayaraghavan, U.A. Rana, D. Fredericks, A. Patti, D. MacFarlane, Dissolution of feather keratin in ionic liquids, Green Chemistry, 15 (2013) 525-534. [36] C.M. Carr, W.V. Gerasimowicz, A carbon-13 CPMAS solid state NMR spectroscopic study of wool: effects of heat and chrome mordanting, Textile Research Journal, 58 (1988) 418-421. [37] M.J. Duer, N. McDougal, R.C. Murray, A solid-state NMR study of the structure and molecular mobility of α-keratin, Physical Chemistry Chemical Physics, 5 (2003) 2894-2899. [38] M. Marti, R. Ramirez, A. Manich, L. Coderch, J. Parra, Thermal analysis of merino wool fibres without internal lipids, Journal of Applied Polymer Science, 104 (2007) 545-551. [39] D. Phillips, Detecting a glass transition in wool by differential scanning calorimetry, Textile Research Journal, 55 (1985) 171-174. [40] M. Zoccola, A. Aluigi, C. Tonin, Characterisation of keratin biomass from butchery and wool industry wastes, Journal of Molecular Structure, 938 (2009) 35-40. [41] E. Bendit, Melting of α-keratin in vacuo, Textile Research Journal, 36 (1966) 580-581.
ACCEPTED MANUSCRIPT Highlights
PT RI SC NU MA D PT E
CE
Chemical free powder fabrication from waste alpaca fibres The finer particle size of 2.5 μm obtained by air jet-milling No chemical changes in functional groups, yet physical damage was observed when fibres converted into powders Reduction of crystallinity index (Cr.I) from around 43% (alpaca fibre) to 27% (air jetmilled powder) Increased moisture absorbing properties with powder particle size reduction
AC
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
Figure 10
Md Abdullah Al Faruque, Rechana Remadevi, Xungai Wang, Maryam Naebe PII: DOI: Reference:
S0032-5910(18)30892-1 doi:10.1016/j.powtec.2018.10.049 PTEC 13824
To appear in:
Powder Technology
Received date: Revised date: Accepted date:
31 August 2018 21 October 2018 23 October 2018
Please cite this article as: Md Abdullah Al Faruque, Rechana Remadevi, Xungai Wang, Maryam Naebe , Preparation and characterisation of mechanically milled particles from waste alpaca fibres. Ptec (2018), doi:10.1016/j.powtec.2018.10.049
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Preparation and characterisation of mechanically milled particles from waste alpaca fibres Md Abdullah Al Faruque, Rechana Remadevi, Xungai Wang and Maryam Naebe* Deakin University, Institute for Frontier Materials (IFM), Geelong, Victoria 3216, Australia
AC
CE
PT E
D
MA
NU
SC
RI
PT
*corresponding author`s email: [email protected]
ACCEPTED MANUSCRIPT Abstract In this work, a chemical free green processing route was followed to fabricate alpaca powders from waste alpaca fibres. The waste fibres were converted into powders with the average particle size of 2.5 μm without using any chemicals neither in pre-treatment nor in powder fabrication process. Despite visible morphological changes of the powder samples, Nuclear
PT
Magnetic Resonance Spectroscopy (NMR) and Fourier Transform Infrared (FTIR) revealed
RI
no chemical change or shift in the functional groups. The crystallinity of the powdered
SC
samples decreased with the reduction of particle size in different stages of the milling process. The differential scanning calorimetry (DSC) and thermogravimetric (TGA) test
NU
results revealed that the thermal stability of the alpaca powder was almost similar to that of alpaca fibre. The air jet-milled powder showed an increase in moisture regain and moisture
MA
content by around 38% and 33% respectively than that of alpaca fibres. The results suggest that alpaca powders have a great potential to be introduced to a wide range of new
PT E
D
applications.
Keywords: Protein fibre; mechanical milling; particle size; characterisation; NMR,
AC
CE
moisture properties.
ACCEPTED MANUSCRIPT
1. Introduction Keratinous and non-keratinous protein fibres are widely used in textiles due to their high quality and accessibility [1]. The waste fibres produced from these sources are enormous. A practical way of breaking down these waste materials is converting the waste fibres into fine
PT
powders to be used in coating, drug delivery, cosmetics, environmental protection, composite
RI
films and fibres preparation [2]. For example, while a very unique way of converting wool
SC
fibres into nano-scale particles was reported, the particles were used as a film on the surface of pure cotton fabric that resulted in changing the functional properties of the fabric [3]. The
NU
cotton fabric coated with the particles showed lower moisture absorbency and increased the thermal retention property compared with uncoated fabric [3]. Wool powder blended
MA
polypropylene fibres were produced with the fineness of around 3 dtex/filament, where by incorporating 2-3% of wool particles, the blended fibres showed greater elastic recovery,
D
moisture and dye-uptake properties than the pure polypropelene fibres [4]. In another work,
PT E
wool fibres were converted into powders by using the air jet-milling technique and the dye/metal ion (Co2+, Cu2+ and Cd2+) absorption capability of the wool powders was studied
CE
[5]. It was found that the moisture absorption of the powdered wool samples reduced while
AC
the dye/metal ion absorption ability of the wool particles increased [5]. It has been reported that pulverized chicken feather particles can act as a bio-sorbent of precious metals (e.g. gold and platinum), capable of controlling water pollution [6] and silk particles have the potential for use in drug delivery and in the cosmetic industry [7]. Moreover, wet milled powder particles, fabricated from cashmere guard hair, were used for the absorption of metal ions (e.g. Zn2+ and Cr6+ ) from the aqueous solution. The cashmere powders were more efficient in absorbing Cr6+ compared with wool and silk powders due to the higher disruption in cuticle cells of guard hair and the higher oxidation of the cashmere powder surface [8].
ACCEPTED MANUSCRIPT The animal protein fibres can be converted into fine powder particles using two different approaches, namely, the chemical or bottom-up approach and the mechanical or top-down approach [9]. In the bottom-up approach, the fibres are dissolved in a suitable solvent that disrupts the intermolecular bonds and solubilizes the fibres and finally, the solution is converted into the fine particles [9]. However, in this method toxic chemicals are often
PT
required to be used which can diminish the natural properties of the fibres and are harmful to
RI
the environment. Moreover, this method is costly and time-consuming [10]. Another
SC
approach, known as the top-down approach, is the mechanical milling process where the natural fibres, like cotton, wool, silk and cashmere or the metal and ceramics, for example,
NU
aluminium (Al) and boron carbide (B4C) are first chopped into small particles. And then by applying different milling techniques like planetary ball milling [11, 12] and wet attritor
MA
milling [13] are ground into fine particles. In this method, the powders can retain or improve the inherent characteristics (e.g. biodegradability, biocompatibility, moisture and dye uptake
D
properties) of fibres [3, 6-8, 13]. Between the two approaches, the top-down approach of
PT E
powder formation is easy, safe, quick and environmentally friendly [9, 12]. Alpaca is a keratinous protein fibre similar to wool, cashmere and other hair fibres in its
CE
physical and chemical characteristics. In addition, it is a special and luxurious fibre with
AC
excellent softness, great warmth, good lustre and strength [14, 15]. Moreover, inherently alpaca fibres come in 22 shades of colour as reported by Fan et al. [16]. It is reported that annually 5000 tonnes of alpaca fibres are produced worldwide.
During shearing and
processing the alpaca fibres, around 20-30% of short and non-spinnable fibres are produced, mostly ending in landfill, fed into incinerator or used as low-grade animal feed [17-19]. Although the converted waste alpaca fibres into fine powder particles may have high potential to be used in different areas, there is no report on powder formation of alpaca fibre. Moreover, as alpaca fibre comes with different shades of colour, the fine alpaca particles
ACCEPTED MANUSCRIPT could also be used as a colour pigment that has not been addressed in literature. In this study and for the first time, waste alpaca fibres were successfully converted into fine powder particles by following the mechanical milling process. Previously different chemical pretreatment techniques were adopted to ease the powder formation process of other protein fibres like cashmere and wool [20, 21]. However, in the current study, no chemical pre-
PT
treatment was implemented neither to accelerate the mechanical milling process nor to reduce
RI
the particle size. A detailed characterisation of the fabricated powder materials from protein
SC
fibres is missing in literature, hindering the proper understanding of potential application areas of the developed protein powders from fibres. Therefore, in this study, the produced
NU
powders from waste alpaca fibres were characterised by their particle size distribution, morphological, structural, thermal and moisture uptake properties to better understand the
MA
newly formed powder materials.
PT E
2.1. Materials preparation
D
2. Materials and methods
Black waste alpaca fibres were supplied by Nocturne Alpacas, Buckley, VIC 3240, Australia.
CE
The mean staple length and diameter of the used alpaca fibre were 65.58 mm and 21 μm, respectively. After removing different impurities such as vegetable matters, the fibres were
AC
washed with commercially available Eucalyptus wool wash as the detergent. Finally, the fibres were rinsed with water and dried in a conventional oven overnight at 60⁰C. 2.2. Powder fabrication The powder fabrication process was carried out by following the method previously explained [13]. Briefly, the dried alpaca fibres were chopped with a rotary cutter mill (Pulverisette 19 from Fritsch GmbH, Germany) to make snippets of approximately 1 mm in length. The snippets were then milled with an Attritor mill (2S, Union Process, USA) to
ACCEPTED MANUSCRIPT produce alpaca slurry. The attritor mill was equipped with a drum containing ceramic balls, an agitator shaft, and sets of impeller (inside of the drum). These impellers were set at right angle to each other, capable of producing higher energy to convert the particles into lowered particle size. Alpaca snippets (200 g) were mixed with 2 litre of deionised (DI) water and fed into the grinding chamber of the attritor mill. During the milling process, the agitator was
PT
kept running at 280 rpm for 6 hrs to convert the snippets into a slurry. After slurry formation,
RI
it was dried by using a laboratory scale mini spray dryer (B-290, Buchi Labortechnik AG,
SC
Switzerland) producing the spray dried powder. The slurry flowed into the dryer at 10 ml/min with the inlet air temperature of 180⁰C and the outlet air temperature of 100⁰C. The spray
NU
dried powders were then passed through the air jet milling process using the laboratory air jet mill (Sturtevant Inc, USA) at 110 PSI grinding air pressure. Digital images of the alpaca fibre
MA
(AF), alpaca snippets (AS), attritor milled slurry (AMS), spray dried powder (SDP) and air jet-milled powder (AJM) samples are shown in Fig. 1. The instruments used in the powder
PT E
D
fabrication method are presented in Fig. 2.
and d) air jet mill.
AC
CE
Fig. 1. Instruments used in powder fabrication: a) cutter mill, b) attritor mill, c) spray dryer
Fig. 2. Digital images of samples: a) alpaca fibres (AF), b) alpaca snippets (AS), c) attritor milled slurry (AMS), d) spray dried powder (SDP) and e) air jet milled powder (AJM).
2.3. Particle size measurement
ACCEPTED MANUSCRIPT The particle size of the alpaca snippets, slurry, spray dried powder and air jet-milled powder was measured by using the Malvern mastersizer 2000, USA fitted with Hydro 2000S. The refractive index of alpaca fibre (1.56) was used during the measurement. Alpaca powders were dispersed in DI water and then added to the mastersizer for particle size measurement. The data was collected after each sample was measured four times. The volume-based
PT
particle size method was adopted to analyse the results, where the volume median diameter
RI
d(0.5) represents that 50% of particles are above and 50% below the stated size. In addition,
SC
d(0.1) and d(0.9) values denote that 10% and 90% of the measured particles were less than the presented size [22]. Error bars were not considered due to insignificant variation in d(0.5)
MA
2.4. Scanning Electron Microscopy (SEM)
NU
measurements per powder sample from the Mastersizer 2000.
The morphologies of alpaca fibres and powders were analysed by using a Zeiss Supra 55VP
D
scanning electron microscope (SEM) at an accelerating voltage of 3 kV. Prior to the imaging,
PT E
all the samples were gold coated using Leica EM ACE600 gold coater. 2.5. Fourier Transform Infrared (FTIR)
CE
The Fourier transform infrared (FTIR) spectra of alpaca fibre and its powder samples were performed under Attenuated Total Reflectance (ATR) mode using Vertex 70 (Bruker,
AC
Germany) spectrometer with a scan resolution of 4 cm-1 and 32 scans per sample between 400 cm-1 and 4000 cm-1. The data was subjected to baseline correction by OPUS software 5.5. 2.6. X-ray diffraction (XRD) The effect of the powder formation process on the crystallinity of the alpaca fibres was analyzed by X-ray diffraction (XRD) technique (X’Pert Powder, PANalytical, Netherlands), at 40 kV operating voltage and current flow of 30 mA. The measurement was taken between
ACCEPTED MANUSCRIPT 6 degrees and 40 degrees; step size was 0.013⁰ and 250s per step. The crystallinity index (Cr.I.) of the parent fibres and the powders was calculated by Equation (1) [23]: Cr.I. = (I9 - I14) * 100 / I9
(1)
where Cr.I. is the crystallinity index, I9 is the maximum intensity in arbitrary units with 2-
PT
theta at 9⁰ and I14 is the maximum intensity in arbitrary units with 2-theta at 14⁰. In general,
SC
2.7. Nuclear Magnetic Resonance Spectroscopy (NMR)
RI
the higher Cr.I. value represents the higher crystallinity of the sample [24].
solid-state
13
NU
The 1H NMR and 13C NMR spectra were recorded on a Bruker spectrometer, Germany. The C CP-MAS NMR spectra of the samples were recorded on a 300 MHz Bruker
MA
Ascend 300 WB spectrometer by using a 4 mm rotor at 10 KHz spinning rate and 1600 scans for each sample. All the data were extracted using TopSpin 3.2 software.
PT E
D
2.8. Differential Scanning Calorimetry (DSC) Differential Scanning Calorimetry (DSC) test was carried out by DSC Q200 (TA Instruments, USA). The samples (5 mg) were heated from ambient temperature to 300⁰C at a
CE
heating rate of 10⁰C/min in a nitrogen atmosphere.
AC
2.9. Thermogravimetric analysis (TGA) Thermogravimetric analysis (TGA) was carried out by using TGA Q50 (TA Instruments, USA), where the samples (5 mg) were heated from room temperature to 600⁰C at a heating rate of 10⁰C/min in a nitrogen atmosphere. 2.10. Moisture properties The percentage of moisture regain (MR) and moisture content (MC) of the alpaca fibres, snippets, spray dried and air jet-milled powders were measured by the ASTM D1576-13
ACCEPTED MANUSCRIPT method illustrated in the literature [25, 26]. Briefly, approximately 2 g of each sample was conditioned at 20⁰C±2⁰C and 62%± 2% RH (relative humidity) for 2 days. The conditioned samples were then weighed and dried at 110⁰C for 4 hours in an oven. The samples were reweighed and moisture regain and content were calculated from Equation (2) and Equation
PT
(3), respectively:
MC (%) = (M-D) / M * 100
RI
MR (%) = (M-D) / D * 100
(2) (3)
SC
where M is the weight of the conditioned sample and D is the weight of the oven-dried
NU
sample. Each sample was tested five times and the result was reported as an average.
MA
3. Results and discussion 3.1. Particle size of the samples
D
The volume-based particle size distribution of the alpaca samples after each step of powder
PT E
formation is shown in Fig. 3. Table 1 shows the particle size values of d(0.1), d(0.5) and d(0.9) at different phases of powder fabrication. It is evident that during snippets and attritor
CE
milled slurry formation the particle size of the fibres reduces. The reduction in particle size of d (0.5) from 70.04 μm to only 2.88 μm during attritor milling can be due to the combined
AC
action of the impellers and ceramic balls inside the milling drum. During the rotation of the agitator shaft inside the drum, the snippets passed through continuous and vigorous beating that reduced the alpaca particle size in the slurry. In contrast, after the spray drying process the particle size of d(0.5) increased to7 μm. This may be due to the particle aggregations at the time of spray drying or loss of finer particles as the slurry passes through the nozzle and the cyclone of the spray dryer [13]. However, it could be possible to break-down the aggregated particles further into a smaller size by using the air jet-milling process. During air
ACCEPTED MANUSCRIPT jet milling, the spray dried powders are fed into an air vessel by a feed plate to further decrease the particle size. The compressed grinding air pressure fed into the chamber creates an air vortex due to high speed which reduces the particle size of d(0.5) to 2.5 μm. It has been reported that the particle size of pigments that can be used as textile colourant, ranges between 1-75 μm [27]. While alpaca fibres are naturally coloured fibres in 22 different colour
PT
shades [16], our group has shown that both the spray dried (7 μm) and air jet-milled (2.5 μm)
RI
powders have high potential to be used as pigments for colouration of regenerated fibres
SC
(unpublished results).
Table 1 The particle size of alpaca powders at different stages of powder formation
Alpaca snippets
20.56
Attritor milled slurry
1.31
Spray dried powder
2.80
Air jet-milled powder
1.10
d (0.5) (μm)
d (0.9) (μm)
70.04
580.45
NU
d (0.1) (μm)
2.88
6.68
7.14
16.63
2.55
6.89
CE
PT E
D
MA
Sample name
Fig. 3. Particle size distribution of alpaca fibre at different stages of mechanical milling;
AC
snippets (AS), slurry (AMS), spray dried powder (SDP) and air jet milled powder (AJM).
3.2. Morphology of alpaca fibre and powders The morphology of alpaca fibre and its powders at different stages of powder formation is shown in Fig. 4. The SEM image of Fig. 4 (a) shows overlapping cuticle scales on the surface of the alpaca fibre similar to wool and other hair fibres [28]. It is observed that when alpaca
ACCEPTED MANUSCRIPT fibres were split by cutter mill into snippets, the scales of the parent fibre were retained without complete destruction of the cuticle as shown in Fig. 4 (b). The spray dried powders look like agglomerated particles in Fig. 4 (c). However, after the air jet milling process the particles were converted into smaller particle size as shown by particle size analysis (Table 1) and Fig. 4 (d). From the SEM images, it is evident that the cuticle, cortex, and microfibrils of
PT
the parent alpaca fibres are significantly destroyed in both the spray dried and air jet-milled
RI
powders. This is due to the extensive wet attritor milling process and also the consecutive
SC
drying processes [13, 20]. While observation of the morphology of alpaca fibres assists in understanding the effect of mechanical milling on powder, the loss in the inner and outer
MA
powders, which will be discussed later.
NU
structure of the fibres can affect the crystallinity and moisture absorbing properties of the
3.3. FTIR analysis
powder.
PT E
D
Fig. 4. SEM images: a) Alpaca fibre, b) snippets, c) spray dried powder and d) air jet-milled
CE
The FTIR analysis of alpaca fibre and its powders produced at different steps is presented in
AC
Fig. 5. The FTIR spectra of powders revealed similar peak positions to the alpaca fibres. No new peaks or peak shifting were found in the functional groups of the powder samples. The region between 1300 cm-1 and 1700 cm-1 represents the protein amide group where peaks at 1450-1500 cm-1 correspond to methyl C-H deformation. In addition, the peak position between 1600 cm-1 and 1700 cm-1 region represents protein amide I of C=H stretching [29]. In general, the peaks at 1648-1660 cm-1, 1540-1550 cm-1, 1235-1250 cm-1 and 3300 cm-1 represent the amide I, amide II, amide III and amide A (N-H stretching) regions of the protein structure, respectively [30]. Another two prominent peaks are 2850 cm-1 and 2930 cm-1
ACCEPTED MANUSCRIPT representing the symmetric and asymmetric C-H stretching vibrations of methylene [31]. In this study, the powder fabrication method was performed by a mechanical milling process without adding any chemicals. Therefore, it can be concluded that the mechanical milling process had no adverse effect on the functional groups of the alpaca fibres.
RI
and air jet-milled powder (AJM).
PT
Fig. 5. FTIR analysis of alpaca fibre (AF), alpaca snippets (AS), spray dried powder (SDP)
SC
3.4. XRD analysis
NU
The diffraction patterns of alpaca fibres and powders are shown in Fig. 6. The crystallinity index values (Cr.I.) of the fibres and powders are also shown in Table 2. The diffraction
MA
pattern of alpaca fibre shows a minor 2θ peak at 9⁰ of crystalline spacing of 9.8 Å and a strong 2θ peak at 20⁰ indicating the crystalline spacing of 4.4 Å [28]. It is well known that the
D
peak at 2θ 9⁰ refers to the α-helix structure while the peak at 2θ 20⁰ corresponds to the β-
PT E
sheet configuration [32]. When the fibres are converted into powders by the mechanical process, the intensity of the minor 2θ peak at 9⁰ gradually reduces and the 2θ peak of 20⁰
CE
becomes broader in range compared to the peak representing the parent alpaca fibre. This steady deterioration and broadening of peaks represent the increase in disoriented areas in the
AC
β-sheet configuration that leads to the lower crystalline structure in smaller particle size samples [12, 33]. Previously, it has been reported that the cuticle which is the outermost layer in protein fibres, possesses the most regular crystalline structure [34]. However, due to attritor milling and subsequent drying processes during powder formation, the outermost layers of the alpaca fibres were completely destroyed in both spray dried and air-jet milled powder. This deterioration in layers maybe accountable for the lower crystalline (Table 2) and subsequent higher amorphous structures in alpaca powders than that of parent fibres [12].
ACCEPTED MANUSCRIPT The higher amorphous region of the powders can be useful where higher moisture properties are required for new applications (e.g pigments). Table 2 Crystallinity index values of alpaca fibres and powders
Crystallinity index (%)
Alpaca fibre (AF)
42.95
Alpaca snippets (AS)
33.18
Spray dried powder (SDP)
29.58
Air jet-milled powder (AJM)
27.03
MA
NU
SC
RI
PT
Sample name
Fig. 6. XRD analysis of alpaca fibre (AF), alpaca snippets (AS), spray dried powder (SDP)
PT E
D
and air jet-milled powder (AJM).
CE
3.5. NMR spectroscopy analysis
The fine structures of alpaca fibres and its powder materials were investigated by solid-state 13
AC
C CP MAS NMR as shown in Fig. 7. The different spectra in Fig. 7 show the typical
asymmetric peak in between 170 and 174 ppm that represents the carbonyl (C=O) group of keratinous material [35, 36]. The peak at 130 ppm refers to various aromatic carbons (C=C) existing in keratin [36]. From Fig. 7, it was also found that all the powder samples retained this similar peak position at 130 ppm, which suggests no disruptions to aromatic regions of the protein fibres while converting to powders through the mechanical milling process. The other two peaks at 55 ppm and 40 ppm represent the α-carbons and β-carbons, respectively.
ACCEPTED MANUSCRIPT The peaks between 25 ppm and 35 ppm are attributed to the alkyl groups of the side chains [36]. It has been reported that β-carbons are mainly present in leucine and cysteine residues and the peaks between 25 ppm and 35 ppm represent carbons in glutamine, proline and glutamic acid residues [37]. From the NMR spectroscopy, it is confirmed that like other keratinous materials, alpaca possesses similar carbon peaks. Consistent with the findings
PT
from FTIR and XRD, NMR results further confirmed neither new chemical bond formation
SC
RI
nor peak shifting occurred in the mechanically milled alpaca powder.
NU
Fig. 7. 13C NMR spectra of alpaca fibre (AF), alpaca snippets (AS), spray dried powder
MA
(SDP) and air jet-milled powder (AJM).
D
3.6. DSC analysis
PT E
The differential scanning calorimetric plots of the samples are shown in Fig. 8. Three thermal events are described by the DSC test such as glass transition, moisture evaporation and
CE
denaturation [38]. The glass transition of the alpaca fibres and powders ranges between 40⁰C
AC
and 60⁰C [38]. From Fig. 8, it is evident that the glass transition temperature of alpaca fibre and snippets is almost identical. On the other hand, spray dried powder shows the highest glass transition temperature and in the case of air jet-milled powder, it is the lowest. This might be due to the agglomeration of the particles. As explained before, during spray drying due to loss of fine particles or agglomeration, the particle size increased in spray dried powders that is further reduced by air jet milling [13]. Therefore, as the particles are more agglomerated in spray dried powders, these are showing higher Tg than others. In addition, the breaking of the agglomerated particles reducing the
particle size, glass transition
ACCEPTED MANUSCRIPT temperature decreased in the air jet milled powder [39]. Similarly, due to the lower particle size and reduced crystallinity, the water evaporation temperature of the air jet-milled powder increases compared to the other samples [38]. The other major peak between 230⁰C and
PT
240⁰C is attributed to crystal disruption of the α-keratinous materials of the fibres [38, 40].
Fig. 8. DSC analysis of alpaca fibre (AF), alpaca snippets (AS), spray dried powder (SDP)
SC
RI
and air jet milled powder (AJM).
NU
3.7. TGA analysis
MA
The thermogravimetric analysis (TGA) of alpaca fibres, snippets, spray dried and air jetmilled powders are shown in Fig. 9. It is evident that the main weight loss took place at temperature ranges from 30⁰C to 120⁰C and 220⁰C to 450⁰C, respectively. The first weight
PT E
D
loss is attributed to the loss of moisture [1]. Generally, because of reduced particle size, the crystalline region is destroyed and amorphous region is increased that promotes a higher moisture absorbing property [1]. It is worth mentioning that the total water evaporation range
CE
between 120⁰C and 150⁰C for very small powdered particles has also been reported [41]. In
AC
this study, the TGA curve can be divided into two stages; one is between 30⁰C and 120⁰C that can be attributed to the loss of water and another one is between 220⁰C and 450⁰C that could be due to the destruction of intermediate protein molecules like hydrogen sulphide and sulphur dioxide [1]. Although the alpaca snippets and air jet-milled powders are showing almost similar thermal behaviour to the parent fibre, the spray dried powder is presenting slightly higher thermal behaviour. As discussed by DSC results, this is also due to the agglomeration of particles in the spray dried powders while fabricating the powders from the fibres. In addition, as the maximum thermal decomposition temperatures of the snippets,
ACCEPTED MANUSCRIPT spray dried powders and air jet-milled powders are not lower than that of parent fibres (Fig. 9), it can be concluded that the thermal stability of the powder particles produced by mechanical milling has not been degraded [1]. Currently, our group is working on fabrication of composite fibres from alpaca powder and polyacrylonitrile (PAN) and it has been found that the thermal stability of the composite fibres enhanced due to higher thermal properties of
PT
the alpaca compared to the PAN (unpublished result). However, previously it was reported
RI
that when wool fibre was converted into powder by using a chemical process, the thermal
SC
stability of the powder deteriorated [10].
NU
Fig. 9. TGA analysis of alpaca fibre (AF), alpaca snippets (AS), spray dried powder (SDP)
MA
and air jet-milled powder (AJM).
PT E
D
3.8. Moisture properties of the alpaca samples The moisture regain (MR) and moisture content (MC) of alpaca fibres, snippets, spray dried powders and air jet-milled powders are shown in Fig. 10. It is observed that with the
CE
reduction in particle size the moisture uptake (%) gradually increases among the powder
AC
samples. This might be due to the reduction in the crystalline region as explained before, thereby enhancing the amorphous region to facilitate penetration of water molecules into the powders that eventually improves the moisture absorbing capacity of the powders. In addition, reduction in the particle size leads to increased surface areas; with the increase in surface area, the number of water molecules peneterating into the powders increases. Similar results were found when wool fibres were converted into fine powders, the particle size reduced and affinity towards water increased [28]. In this study, the air jet-milled powder shows a higher moisture regain (20.13%) and moisture content (16.59%) than the other
ACCEPTED MANUSCRIPT powders and alpaca fibres. Therefore, as the powder exhibited enchanced moisture properties, based on the final application and as required seems that it can be applied to any synthetic polymer to enhance the moisture properties.However, an exception was found while the wool fibres were converted into powders for dye and metal ion sorption [5]. The author reported lower moisture absorption properties because of higher cystallinity of the powders, although
PT
the crystallinity index was not calculated. In addition, from the author’s X-ray photoelectron
RI
spectroscopy (XPS) analysis, it was found that with the reduction in particle size, the carbon
SC
(C) content was decreased from around 78% to 66% and oxygen (O) content was increased from approximately 11% to 18% that ensures the high water absorption tendency of the wool
NU
powders. Moreover, the author also mentioned that during the milling process the cuticle cells of the fibres were destroyed and the cortex of the fibres exposed which may also be
MA
responsible for the higher moisture absorption. It is not completely clear why this
PT E
D
phenomenon was reported.
Fig. 10. Moisture regain (%) and moisture content (%) of alpaca fibre (AF), alpaca snippets
AC
4. Conclusion
CE
(AS), spray dried powder (SDP) and air jet-milled powder (AJM).
In this study, the waste alpaca fibres were converted into powders by the mechanical milling process without any chemical pre-treatment. It was found that the particle size of the fibres was gradually reduced at every step of the milling process although it increased during the spray drying process due to agglomeration of the particles. While the morphological analysis confirmed that mechanical milling is capable of producing the fine powder particles from the fibres, the smallest particle size of 2.5 µm was found after the air jet-milling. Chemical
ACCEPTED MANUSCRIPT analysis revealed no chemical changes or peak shifting in functional groups of the powder compared to the alpaca fibres. As a result, it is expected that the inherent properties of the fibres is retained. However, the crystallinity of the powders reduced gradually due to the lower particle size. Thermal analysis further confirmed that the thermal stability of the powder particles did not deteriorate compared to the parent fibre. The alpaca powders showed
PT
an increase in moisture properties over that of the parent fibres. These findings will help the
RI
possible development of certain application areas of alpaca powders, such as fabricating
SC
pigments for colouration, or manufacturing composite films or fibres with enhanced moisture and thermal properties.
NU
Acknowledgement
MA
The current study was supported by Deakin University Postgraduate Research Scholarship (DUPRS) awarded to the first author, and was carried out with the support of the Deakin
AC
CE
PT E
D
Advanced Characterization Facility.
ACCEPTED MANUSCRIPT References
AC
CE
PT E
D
MA
NU
SC
RI
PT
[1] W. Xu, W. Guo, W. Li, Thermal analysis of ultrafine wool powder, Journal of Applied Polymer Science, 87 (2003) 2372-2376. [2] K. Patil, R. Rajkhowa, X. Wang, T. Lin, Review on fabrication and applications of ultrafine particles from animal protein fibres, Fibers and Polymers, 15 (2014) 187. [3] J. Hu, Y. Li, Y. Chang, K. Yeung, C. Yuen, Transport properties of fabrics treated with nano-wool fibrous materials, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 300 (2007) 136139. [4] G. Xushan, Development of wool powder/polypropylene blend fibers, Melliand International, 12 (2006) 267. [5] G. Wen, Characterization and sorption ability of wool powder, Institute for Frontier Materials, Deakin University, Geelong, Victoria, Australia, 2009, pp. 1-134. [6] K. Suyama, Y. Fukazawa, H. Suzumura, Biosorption of precious metal ions by chicken feather, Applied Biochemistry and Biotechnology, 57 (1996) 67. [7] T. Une, K. Kusaki, T. Hiroyuki, Properties of silk pigments and its use for cosmetics, Fragrance Journal, 4 (2000) 15-21. [8] K. Patil, S.V. Smith, R. Rajkhowa, T. Tsuzuki, X. Wang, T. Lin, Milled cashmere guard hair powders: Absorption properties to heavy metal ions, Powder Technology, 218 (2012) 162-168. [9] M. Kazemimostaghim, R. Rajkhowa, X. Wang, Comparison of milling and solution approach for production of silk particles, Powder Technology, 262 (2014) 156-161. [10] K. Wang, R. Li, J. Ma, Y. Jian, J. Che, Extracting keratin from wool by using L-cysteine, Green Chemistry, 18 (2016) 476-481. [11] A. Canakci, T. Varol, F. Erdemir, S. Ozkaya, New Coating Technique for Al–B 4 C Composite Coatings by Mechanical Milling and Composite Coating, Powder Metallurgy and Metal Ceramics, 53 (2015) 672-679. [12] F. Erdemir, Study on particle size and X-ray peak area ratios in high energy ball milling and optimization of the milling parameters using response surface method, Measurement, 112 (2017) 53-60. [13] R. Rajkhowa, Q. Zhou, T. Tsuzuki, D.A. Morton, X. Wang, Ultrafine wool powders and their bulk properties, Powder Technology, 224 (2012) 183-188. [14] X. Wang, L. Wang, X. Liu, The quality and processing performance of alpaca fibres: A report for the rural industries research and development corporation, RIRDC Publication, (2003). [15] C. Lupton, A. McColl, R. Stobart, Fiber characteristics of the Huacaya Alpaca, Small Ruminant Research, 64 (2006) 211-224. [16] R. Fan, G. Yang, C. Dong, Study of hair melanins in various hair color Alpaca (Lama Pacos), AsianAustralasian Journal of Animal Sciences, 23 (2010) 444-449. [17] A. Shavandi, T.H. Silva, A.A. Bekhit, A.E.-D. Bekhit, Dissolution, Extraction and Biomedical Application of Keratin: Methods and Factors Affecting the Extraction and Physicochemical Properties of Keratin, Biomaterials Science, (2017). [18] Y. Zhang, R. Yang, W. Zhao, Improving digestibility of feather meal by steam flash explosion, Journal of Agricultural and Food Chemistry, 62 (2014) 2745-2751. [19] S. Huda, Y. Yang, Feather fiber reinforced light-weight composites with good acoustic properties, Journal of Polymers and the Environment, 17 (2009) 131. [20] K. Patil, R. Rajkhowa, X.J. Dai, T. Tsuzuki, T. Lin, X. Wang, Preparation and surface properties of cashmere guard hair powders, Powder Technology, 219 (2012) 179-185. [21] Y. Cheng, C. Yuen, Y. Li, S. Ku, C. Kan, J. Hu, Characterization of nanoscale wool particles, Journal of Applied Polymer Science, 104 (2007) 803-808. [22] G. Niro, GEA Niro Method No, A, 2005. [23] S. Zheng, Y. Nie, S. Zhang, X. Zhang, L. Wang, Highly efficient dissolution of wool keratin by dimethylphosphate ionic liquids, ACS Sustainable Chemistry & Engineering, 3 (2015) 2925-2932.
ACCEPTED MANUSCRIPT
AC
CE
PT E
D
MA
NU
SC
RI
PT
[24] H. Xu, Y. Yang, Controlled de-cross-linking and disentanglement of feather keratin for fiber preparation via a novel process, ACS Sustainable Chemistry & Engineering, 2 (2014) 1404-1410. [25] R. Remadevi, S. Gordon, X. Wang, R. Rajkhowa, Investigation of the swelling of cotton fibers using aqueous glycine solutions, Textile Research Journal, 87 (2017) 2204-2213. [26] A.S.T.M., Standard Test Method for Moisture in Wool by Oven-Drying, D1576-13, ASTM International, West Conshohocken, PA, 2013. [27] A.M. Gueli, G. Bonfiglio, S. Pasquale, S.O. Troja, Effect of particle size on pigments colour, Color Research & Application, 42 (2017) 236-243. [28] W. Xu, W. Cui, W. Li, W. Guo, Development and characterizations of super-fine wool powder, Powder Technology, 140 (2004) 136-140. [29] R. Li, D. Wang, Preparation of regenerated wool keratin films from wool keratin–ionic liquid solutions, Journal of Applied Polymer Science, 127 (2013) 2648-2653. [30] A. Aluigi, M. Zoccola, C. Vineis, C. Tonin, F. Ferrero, M. Canetti, Study on the structure and properties of wool keratin regenerated from formic acid, International Journal of Biological Macromolecules, 41 (2007) 266-273. [31] J.-H. Hsu, S.-L. Lo, Chemical and spectroscopic analysis of organic matter transformations during composting of pig manure, Environmental Pollution, 104 (1999) 189-196. [32] E. Bendit, A quantitative x-ray diffraction study of the alpha-beta transformation in wool keratin, Textile Research Journal, 30 (1960) 547-555. [33] G. Jeffrey, J. Sikorski, H. Woods, The Mechanism of Supercontraction in Keratin, Textile Research Journal, 25 (1955) 714-722. [34] I. Fouda, M. El-Tonsy, H. Hosny, Effect of the oxidative power of iodination on the optical properties of Alpaca fibres, Polymer Degradation and Stability, 46 (1994) 287-294. [35] A. Idris, R. Vijayaraghavan, U.A. Rana, D. Fredericks, A. Patti, D. MacFarlane, Dissolution of feather keratin in ionic liquids, Green Chemistry, 15 (2013) 525-534. [36] C.M. Carr, W.V. Gerasimowicz, A carbon-13 CPMAS solid state NMR spectroscopic study of wool: effects of heat and chrome mordanting, Textile Research Journal, 58 (1988) 418-421. [37] M.J. Duer, N. McDougal, R.C. Murray, A solid-state NMR study of the structure and molecular mobility of α-keratin, Physical Chemistry Chemical Physics, 5 (2003) 2894-2899. [38] M. Marti, R. Ramirez, A. Manich, L. Coderch, J. Parra, Thermal analysis of merino wool fibres without internal lipids, Journal of Applied Polymer Science, 104 (2007) 545-551. [39] D. Phillips, Detecting a glass transition in wool by differential scanning calorimetry, Textile Research Journal, 55 (1985) 171-174. [40] M. Zoccola, A. Aluigi, C. Tonin, Characterisation of keratin biomass from butchery and wool industry wastes, Journal of Molecular Structure, 938 (2009) 35-40. [41] E. Bendit, Melting of α-keratin in vacuo, Textile Research Journal, 36 (1966) 580-581.
ACCEPTED MANUSCRIPT Highlights
PT RI SC NU MA D PT E
CE
Chemical free powder fabrication from waste alpaca fibres The finer particle size of 2.5 μm obtained by air jet-milling No chemical changes in functional groups, yet physical damage was observed when fibres converted into powders Reduction of crystallinity index (Cr.I) from around 43% (alpaca fibre) to 27% (air jetmilled powder) Increased moisture absorbing properties with powder particle size reduction
AC
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
Figure 10