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Spray coating of nanocellulose on paper
1. RAPID METHOD OF PREPARING
NANO-CELLULOSE SHEET USING
SPRAY COATING
S.Kirubanandan
Graduate Student
Department of Chemical Engineering,
Monash University, Clayton, Vic 3800
26th August 2016, BAMI Industry Transformation Research Hub Review Seminar
Supervisors: Dr. Warren Batchelor, Prof. Gil Garnier and Dr. Swambabu Varanasi
2. Objective
Spray Coating – A Novel Sheet Making Process
Basis Weight of the Sheet
Uniformity
Surface appearance
Conclusion
OUTLINE
3. SCOPE OF THE WORK
• Developing a spray coating method (Lab Scale) for
preparation of nanocellulose sheets on the stainless steel
plate.
• Evaluating the uniformity using thickness mapping.
• Evaluating the surface characteristics and appearance of the
spray coated nanocellulose sheets.
4. PROCESSING TIME IN CONVENTIONAL PROCESS
Processing Method Processing Time Basis Weight (g/m2)
Spray Deposition 10 -27 mins 13.7 – 124
Vacuum Filtration 3 mins 56.4
Membrane Filtration 55 mins 56
Filter paper based
Filtration
˜48 hrs ND
Fabric Filtration 1- 3 hrs 55
Current Spray Coating* < 1 minute 52.8 -193.0
* Excluding drying time of the sheets
5. SPRAY COATING PROCESS
Spray Coating Provided uniform surface on the
substrate.(Sanna Tiekstra, 2012, Functional Bio
Based Coating for Moulded Pulp Trays,
www.cepi.org)
A Professional spray gun for performing
spray coating process
6. VISCOSITY OF MFC
0
5
10
15
20
25
30
35
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
ViscosityinDIN-Seconds
Concentration of MFC in Wt.%
The liquids are not sprayed properly through the
nozzle of the spray gun. The viscosity of spraying
liquids should be less than 30 DIN -Seconds
The MFC suspension is capable to spray thro
nozzle of the spray gun for the purpose of spray
7. EXPERIMENTAL SET UP
A Professional spray gun for performing spray
coating process
Stainless Steel Plate
Spray Jet of Nano cellulose
from the nozzle (517)
Professional Wagner
System 117
Spray Coated
Nano cellulose
Film
Professional Spray Gun
8. SUSPENSION CONSISTENCY VS BASIS WEIGHT &
THICKNESS
0
50
100
150
200
250
300
0
50
100
150
200
250
0.8 1 1.2 1.4 1.6 1.8 2 2.2
ThicknessinMicrons
BasisWeighting/m2
Concentration of Nanofibrillated Cellulose in Wt%
Basis Weight Vs Suspension Concentration
Thickness Vs Suspension Concentration
10. THICKNESS DISTRIBUTION
Spray Coated MFC Sheets MFC Sheet made by Vacuum Filtration
1 2 3 4
1
2
3
4
Region
Region
111.0
116.0
121.0
126.0
131.0
136.0
141.0
146.0
151.0
1 2 3 4
1
2
3
4
Region
Region
109.0
111.4
113.8
116.1
118.5
120.9
123.3
125.6
128.0
11. SURFACE APPEARANCE OF THE MFC SHEET
Rough Surface Smooth Surface
SEM image of the nano-fibrillated sheet – Rough and Smooth surface at 1µm scale
12. Rough Surface Smooth Surface
SEM image of the nano-fibrillated sheet – Rough and Smooth surface at 10 µm scale
SURFACE APPEARANCE OF THE MFC SHEET
13. Rough Surface Smooth Surface
SEM image of the nano-fibrillated sheet – Rough and Smooth surface at 100 µm scale
SURFACE APPEARANCE OF THE MFC SHEET
14. AFM STUDIES ON THE SHEET
Rough Smooth
AFM Image of the nano-fibrillated sheet – Rough and Smooth surface at 500 nm
15. AFM STUDIES ON THE SHEET
Rough Smooth
AFM Image of the nano-fibrillated sheet – Rough and Smooth surface at 2 µm
16. Surface Roughness of the sheet
Technique used Surface RMS Roughness (nm)
AFM Rough 414.0 nm (10µm
x10µm)
51.4 nm (2µm x
2µm)
Smooth 81.1 nm (10µm
x10µm)
16.7 nm (2µm x
2µm)
Parker Print
Surface
Instrument
Roughness 10.8±0.17µm -
Smoothness 5.5±1.4 µm -
Parker Print
Surface
Instrument
Sheet prepared
via the vacuum
filtration
10.6±0.3 µm
9.9±0.1 µm
-
17. CONCLUSION
• A rapid technique to prepare the nano-cellulose
sheet was developed.
• The sheet has better uniformity and two different
surface.
18. ACKNOWLEDGEMENT
• Dr. Warren Batchelor and Prof. Gil Garnier
• Dr. Swambabu Varanasi
• Mr. Scot Sharman, Mr. Shaun Ang and Ms.
Natasha Yeow
28. Surface Roughness of the nanocellulose
sheet
0
2
4
6
8
10
12
14
40 50 60 70 80 90 100 110
SurfaceRoughnessandSmoothnessinµm
Grammage in GSM
Grammage Vs Roughness
Grammage Vs Smoothness
Editor's Notes
Good Afternoon,
I had like to talk about the rapid preparation of the micro fibrillated sheet on the stainless steel plate using a laboratory scale spray coating method. Past decade cellulose nanofiber sheets plays a major role in the development of sustainable materials used in various fields. The laboratory scale preparation and characterization of cellulose nano fibres sheet is a challenging task. Vacuum filtration which has low drainage time and prepared sheets via this method can be difficult to peel off from the filter and can be hard to handle.
This work reports a rapid preparation technique for nano-cellulose sheets using a bench scale spray coating nanocellulose suspension onto the stainless steel plates. After spraying nanocellulose suspension, the sheets can be dried directly on the plates using standard laboratory procedures, saving processing time and effort. By controlling the spraying time, we were able to produce sheets with a basis weight of 52.8±7.4 to 193.1±3.4 g/m2 when spraying at a conveyor velocity of 0.32 cm/sec. The preparation time for the nano-fibre sheet delivered here was ˜ 1.0 min as minimum processing time though the production times reported in the previous literature is 10 mins. Comparing the uniformities of sheets made by spray coating with those made by vacuum filtration showed high thickness, good basis weight and quality. Thus, the least preparation time for producing the nano-fibrous sheet recommends that this spray coating technique can be utilized for the development of a scalable process for the fabrication of various functional materials.
In this work,
I have developed the spray coating method ( A Laboratory Scale) for preparation of nanocellulose sheets on the stainless steel plate,
Advantages of the Spray Coating
Contactless
Contour coating
Coating of tear sensitive material
Controlling the coating material
This plot explains effect of suspension concentration on the basis weight of the sheet and thickness of the sheet /nanocellulose film prepared using spray coating technique at a constant velocity of 0.32 cm/sec.
The stable and homogeneous films with various concentrations of MFC suspension were prepared via spray coating technique as described in the experimental section. The operational range for spraying nanocellulose suspension was between 1.0 wt. % and 2.0 wt. %. Below 1 wt. %, the suspension was too dilute and flowed over the metal surface, producing a highly uneven film that was difficult to peel from the plate after drying. Above 2% wt. of suspension, the suspension become too viscous to spray. The lower and upper limits, corresponded to suspension viscosities of 17 to 32 DIN sec, respectively.
Mapping of thickness of the nanocellulose sheet which diameter of 15.4 cm. The thickness is measured six locations in each region of the sheet. The rectangular section of centre part of the sheet is used for contour plotting.
The uniformity of the spray coated MFC film is evaluated and compared using contour plot of thickness measured on the various regions of the film and compared with a film made by vacuum filtration.
Figure 3 explains the thickness distribution of the 1.5 Wt. % spray coated film at a constant velocity of 0.0032 m/sec. and film made by vacuum filtration method. The basis weight of the sheet prepared by spray coating and vacuum filtration are 100.5±3.4 g/m2 and 95.2±5.2 g/m2 respectively.
Figure 4 explains the surface morphology and topography of both sides of the spray coated nano-cellulose film investigated by scanning electron microscopy. The spraying nanocellulose on the stainless steel plate produces a rough and smooth side of the sheet. The rough side of the spray coated sheet is similar to the sheet prepared via vacuum filtration. The surface exposed to atmosphere is called rough surface where the residual cellulose fibres are free and roughness in the surface. The rough surface of the film confirms that the film contains densely packed various size of free fibres and clumps of cellulose fibres and further free from pinhole.
Figure 4 shows the rough side of the Nano cellulose film (free surface) that is the side directly to contact with atmospheric. Moreover, the surface of the film is asymmetric structure exclusively the pore size on the rough surface differed from the smooth surface. The fibres are well connected between different fibres size and forms matrix of different pore size. In the rough side of the sheet, there are free fibres towards the atmospheric and high surface roughness. The surface roughness of the nano-fibrillated sheet for rough surface is found to be 10.8±0.17µm. When compared with the surface roughness of reference MFC film made by vacuum filtration (9.9±0.1and 10.6±0.3 both sides), the surface roughness of the spray coated sheet (rough side) is equivalent to the reference sheet.
The glossy and smooth side of the MFC sheet is surface exposed to the stainless steel and the fibres are compressed with hydrophobic surface of steel plate to produce the glossy surface. The surface smoothness of the smooth side of the sheet is 5.5±1.4 µm.
The surface morphology and topography of the nanocellulose sheet evaluated by Atomic force microscopy.
The AFM Studies confirms surface roughness of the sheet prepared via Spraying
The atomic force microscopy investigation of the spray coated nanocellulose film confirms the surface roughness of both side at nano scale. Figure 4 also shows the surface topography of the rough and glossy side of the cellulose film. The surface roughness of the rough side in root mean square (RMS) is 414.0 nm for 10µm x10µm film area and 51.39 nm for 2µm x 2µm film area where as the surface roughness of the glossy side in root mean square (RMS) is 81.05 nm for 10µm x10µm film area and 16.73 nm for 2µm x 2µm film area. Based on the surface roughness in RMS and AFM image, most of the variations in the surface topography and roughness between rough and glossy side of the cellulose film seems to be caused by residual fibres that produce unevenness at surface of the cellulose film. Moreover, Micro-fibrillated cellulose consists of different size of cellulose fibrils and clumps of cellulose fibres have dimension 5-60 nm with several micrometres in length. In the spraying process, the random deposition of cellulose fibres on the steel plate cause the variations in the surface roughness.
The results reported in this investigation confirm that a laboratory scale spraying of various concentration of nano-cellulose on a stainless steel could be considered for the rapid preparation of nano-cellulose film with basis weight ranging from 50 to 200g/m2. The basis weight of the sheet is controlled by the concentration of Nano-cellulose sprayed on the stainless steel plate at a constant speed of conveyor. Moreover, the spraying nanocellulose on the stainless steel plate creates a uniform thickness of the cellulose sheet on the base and its uniformity thro thickness mapping compared with the sheet prepared via vacuum filtration.
The thickness and mass of the film per unit area evaluated in this spray coating method are comparable to that in the work (Beneventi, Zeno et al. 2015) who reported that the thickness and mass per unit area (grammage) of the micro- fibrillated is 30-90µm and 13.7 -124 g/m2, respectively. (Beneventi, Zeno et al. 2015) reported that the processing time for making MFC sheet on nylon fabric varies from spraying time 15 to 90 s to make sheets with the basis weight of 13.5 and 124 g/m2. Their works lacks about how does spraying produce uniform sheet and thickness mapping of the sheet. In our investigation on spraying, the processing time for 1.5 Wt. % of the nano-cellulose sheet is varied from 25 sec to 63 sec to make sheets with basis weight from 49.11±5.39 g/m2 to 102.24 ±7.53 g/m2. Our work is compared with the work reported by (Varanasi and Batchelor 2013), informed that their processing time is 10 min and achieved basis weight of 56.4 g/m2. Moreover, another laboratory method could produce low mass per unit area of the film , for example,(Syverud and Stenius 2008) reported that the prepared 0.1 MFC film has 17-35 g/m2 with a film thickness of 21 ± 1µm to 33 ± 2 µm. The standard method using British Hand Maker could produce the Nano fibrillated film with a basis weight of 62.4 g/m2 (González, Alcalà et al. 2014). Another comparison with the standard method for Nano fibrillated film (Österberg, Vartiainen et al. 2013) has a processing time of 1-2.5 hrs with a basis weight of 55g/m2. Additionally, this laboratory spray coating could be comparable with conventional paper sheets production via rapid kothen sheet maker to produce the sheet with basis weight of 35g/m2 and 28 g/m2 (Beneventi, Chaussy et al. 2014, Beneventi, Chaussy et al. 2014). It does justify the limitations of conventional paper machine and advantages of the spray coating process in the aspects of basis weight and processing time.
The surface morphology of the MFC film characterized by SEM confirms that the presence of difference fibre size and particles . To conclude that the laboratory scale of spray coating to prepare the nano-cellulose sheet is a rapid method and scalable for industrial production.
A rapid and commercially scalable, economically feasible method for preparing nanocellulose sheet is developed to produce high basis weight and quality nanofiber sheet and to replace the standard method of vacuum filtration. The basis weight is controlled by the spraying time and nanocellulose concentration in the suspension. The processing time for producing the sheet is less than 1 min and the quality of the spray coated sheet is confirmed by the uniformity in thickness of the sheet.
I would like to thank my supervisor for guiding this work successfully.
