Progress 09/01/09 to 08/31/12
Outputs
OUTPUTS: The ultimate goal of this research is to develop innovate nanocomposite surface coatings which exhibit low surface energy and minimize biological fouling on food contact surfaces. Anti-fouling attributes of nanocomposite coatings were evaluated in two distinct fouling situations occurring in food processing, specifically, milk protein deposition during pasteurization and bacterial adhesion. A miniature plate heat exchanger (PHE) was designed and built to fulfill the needs of milk fouling tests. PHE's surface was coated with hydrophobic (polytetrafluoroethylene or PTFE, water contact angle or WCA 119.6 deg) and superhydrophobic (5% w/w carbon nanotube or CNT in PTFE matrix, WCA 141.1 deg) surface coatings. Surface energy values estimated for PTFE and CNT-PTFE nanocomposite surfaces were 4.61 mN/m and 0.89 mN/m, respectively. It should be noted that the nanocomposite coating with 5% CNTs (w/w) reduced the surface energy close to zero, which was only achievable by aligned CNT coating technique in the past. Self-cleanability of the CNT-PTFE surface was observed using water drop test. The slow-motion video unveiled the lotus effect of the superhydrophobic coating. The water droplet falling on the CNT-PTFE nanocomposite coated surface actually had sufficient momentum to leave the surface, making several more bounces, eventually bounced off without ever coming to rest on the surface (video component, http://www2.hawaii.edu/~soojin/cnt). Weighed foulants on CNT-PTFE nanocomposite surface after 5h of continuous milk pasteurization was 70% lower than the control. CNT-PTFE PHE system also used 10% less energy than the uncoated PHE due to less insulation effect of surface foulant. The second phase of this research was aimed to test and compare the amounts of bacteria adhered on superhydrophobic and superhydrophilic nanocomposite surfaces under different fluid flow conditions. The adhesion tests were performed in a custom designed parallel flow channel with uncoated steel, 20%w/w CNT-PTFE coated (WCA 154.6 deg, superhydrophobic) and titanium dioxide or TiO2 (WCA 0 deg (superhydrophilic) coated. Surface coated by TiO2 was microscopically smooth by presence of micropillae structure having the average roughness (ra) of TiO2 of 1.1 nm. It can be seen that three-dimensional micropapillae networks on TiO2 coated plate accommodated water to instantly spread onto TiO2 coated surface mainly due the formation of tightly bounded water layer near superhydrophilic surface. E. coli K-12 solution (3x10^8 cells/ml) was pumped through the test unit for an hour at the flow rates of 0 (stagnant) and 200 ml/min (wall shear rate 16,000 per sec), separately. The fluorescence intensity (FI) measurement illustrated that anti-adhesion mechanisms on superhydrophobic and superhydrophilic surfaces were significantly different from each other. The TiO2 plate had the lowest FI value among three surfaces in the stagnant or dry environment (65% lower than control). On the other hand, the FI value for CNT-PTFE surface was 80% lower than control in a continuous mode due to little surface energy nature of superhydrophobic surface. PARTICIPANTS: Natthakan Rungraeng, PhD candidate Department of Molecular Biosciences and Bioengineering, University of Hawaii at Manoa,Honolulu, Hawaii 96822, USA Suk Hoo Yoon, PhD Korea Food Research Institute, Seongnam-si, Republic of Korea Wonyoung Song, PhD AFM Specialist NanoFocus, Inc., Seoul, Republic of Korea TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
The developed nanocomposite coating technique has a great potential for food industry, in particular for dairy applications. Building up of milk foulant on plate heat exchanger (PHE) surface during pasteurization might cause under-processing of milk due to the insulation effect. Therefore, more energy, up to 18% in addition, may be required to ensure milk temperature reaches standard pasteurization temperature, 72 deg C. The developed nano-coating technique is expected to reduce the frequency of routine CIP processes to insure the chemical-exempt food product, minimization of water usage, and reduction in the use of cleaning agents. Therefore, the developed coating technique will be able to make thermal food processing more sustainable in terms of water use, environmentally friendliness,energy savings, and minimized food waste.
Publications
- Choi, W., Jun, S., Nguyen, L.T., Rungraeng, N., Yi, H., Balasubramanian, S., Puri, V.M., & Lee, J. (2012). 3-D milk fouling modeling of plate heat exchangers with different surface finishes using computational fluid dynamics codes. Journal of Food Process Engineering, DOI: 10.1111/j.1745-4530.2012.00684.x
- Rungraeng, N., Cho, Y.C., Yoon, S.H., & Jun, S. (2012). Carbon nanotube-polytetrafluoroethylene nanocomposite coating for milk fouling in plate heat exchanger. Journal of Food Engineering, 111, 218-224.
- Rungraeng, N., & Jun, S. (2012). Superhydrophobic and superhydrophilic nanocomposite coatings for preventing microbial adhesion in liquid food flow channel. IFT Annual Meeting & Food Expo, Las Vegas, NV.
|
Progress 09/01/10 to 08/31/11
Outputs
OUTPUTS: The main objective of this project in 2011 was aimed to explore the capability of developed surface coating in a lab scale plate heat exchanger. The experimental setup was built to demonstrate the surface deposition phenomenon in a plate heat exchanger during milk and pasteurization. The heat exchanger unit composed of a continuous heating section made up of industrial grade stainless steel plate. Two various surface coating materials, namely polytetrafluoroethylene (PTFE) and the combination of PTFE and carbon nanotubes (CNTs) at 5% wt/wt CNT-PTFE, were uniformly annealed on the heat exchanger surfaces. PTFE is well recognized as one of low surface energy materials. Thus, when being used as a heat exchanger surface coating it can exhibit the non-stick phenomenon, resulting in less amounts of milk deposits. Additionally, the anti-fouling attribute of PTFE was enhanced by mixing with CNTs before annealing process. Existence of dispersed CNTs in the PTFE structure significantly increased the nano/microscale surface roughness, resulting in the improvement of hydrophobic characteristics of the PTFE coating. According to the results, a weighed deposit mass on the control surface after the first hour run was 1.51 grams and linearly increased to 2.82 and 4.00 grams after 3 and 5 hours of pasteurization. However, the deposition rates were reduced down when coated surfaces were tested, depending on their surface energy or roughness. For PTFE coating, the masses of milk deposits on uncoated collected after a continuous flow of milk for 1, 3 and 5 hours were 1.51, 1.18, 1.77 and 2.28 grams, respectively. For CNT-PTFE nanocomposite surface, the protein nucleation on CNT-PTFE coating was weak and slow, compared to uncoated and PTFE coated surfaces. Therefore, the shear force of milk stream to flow over the surface could easily sweep away protein molecules deposited from surface. Low nucleation rate and corresponding inhibition of milk deposition at the same operation hours were found. Weighed deposits on CNT-PTFE surface were 0.32, 1.08 and 1.19 grams, respectively. However, for industrial implementation, the completeness of this study can be further fulfilled by investigation of the wear resistance of developed surface coatings. PARTICIPANTS: Soojin Jun, Assistant Professor, Department of Human Nutrition, Food and Animal Sciences, University of Hawaii Natthakan Rungraeng, Graduate Student, Department of Molecular Biosciences and Bioengineering, University of Hawaii Yoon-Chul Cho, Professor, Department of Photographic Arts, Sunchon National University, Sunchon-si, Republic of Korea TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Since the development of milk deposition during pasteurization could retard appropriate heat transfer to adjacent PHE surfaces, which would cause an increase in energy requirement of dairy industries by around 8%. Therefore, this outcome clearly introduces a new approach to reduce the surface deposition rate of milk protein on heat exchanger surfaces by manipulating the surface energy using the nanotechnology. The developed nano-scale surface coating technique has a great potential for dairy applications because the surface deposition always creates the need for frequent cleaning-in-place (CIP) processes to keep the heating surfaces clean. Therefore, the developed coating technique could promisingly reduce the frequency of routine CIP processes to ensure the chemical-exempt food product, minimization of water usage, and reduction in the use of cleaning agents.
Publications
- Rungraeng, N, & Jun, S. (2011). Polytetrafluoroethylene-based carbon nanotube coating for non stick surface in plate heat exchanger. IFT Annual Meeting & Food Expo, New Orleans, LA.
- Rungraeng, N, & Jun, S. (2011). Polytetrafluoroethylene-based carbon nanotube coating for non-stick surface in plate heat exchanger. The 23rd Annual CTAHR Students Symposium, Honolulu, HI.
- Rungraeng, N, Cho, Y.C., & Jun, S. (2011). Lotus effects on uncoated stainless steel and coated with CNT-PTFE. [Flash video]. Retrieved from http://www2.hawaii.edu/~soojin/cnt
|
Progress 09/01/09 to 08/31/10
Outputs
OUTPUTS: The preliminary activity on fouling reduction was studied on the stainless steel surface. A rectangular piece of stainless steel plate in a prototyped miniature plate heat exchanger unit (1:10 downscale) was used as a heat exchanger surface representative. The polytetrafluoroethylene (PTFE) coating layer in 15 micron thickness dramatically increased the static contact angle of water droplet on the stainless steel surface from 70 to 118 degree. The electrical resistive heater was used as the heating source for the developed heat exchanger. Three pieces of 300 W heaters were attached to the outer side of stainless steel surface. Surface temperature and heat flux of stainless steel plate controlled by variac transformer was ranging 60-80 deg C and 600 - 900 W. Adjustable flow rates that peristaltic pump used to deliver the juice into the heat exchanger were between 20 and 200 ml/min. A scanning electron microscopic image of fouling obtained by this custom-designed plate heat exchanger contained numerous bubbles on the nanoscale scratchy surface including lots of cracks and crevices. In addition, the numerical simulation study on the occurrence of fouling in 3D environment was also performed. The realistic corrugated plate profile was implemented using the AutoCAD software. The numerical simulation was performed by computational fluid dynamic (CFD) codes, FLUENT 6.3. The localized velocity and temperature profiles of juice along with predicted deposit distribution were obtained. It is found that the hydrophobic coating materials on heat exchanger surface play an important role to reduce surface fouling. Ongoing research activities are the development of superhydrophilic coating material by adding CNT powder into PTFE matrix. This combined material can be done by two methods: 1) dispersing of CNT powder in PTFE solution by using ultrasonication mixer and 2) using the hot filament chemical vapor decomposition (HFCVD) method. The anti-fouling performances of heat exchanger surfaces influenced by these two samples will be compared in the next round. PARTICIPANTS: Natthakan Rungraeng, a graduate student, was trained for carbon nanotube coating, contact angle measurement, and computational fluid dynamics (CFD) simulation. TARGET AUDIENCES: Dairy and juice industries which intensively use plate heat exchanger systems for the pasteurization process will be targeted audiences since this technology is aimed to minimize the foulant deposition onto the heat exchanger surface, eventually leading energy savings and cost effective practices. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Fouling is a common problem for both conventional (PHE) and emerging (PEF and ohmic heating) pasteurizers since the product after treatment may become contaminated with pieces of the fouling layer that detach from the electrode or walls. Note that developed biofilms could not only provide favorable growth conditions for pathogens but cause the juice products under-processed. If successful, the PTFE-based CNT surface coating will ensure the microbiological quality of fluid food products by keeping biofilms from developing, furthermore, providing the potential and promise to pave the way for new microbial safety practices in the US tropical juice industry.
Publications
- No publications reported this period
|
|