Progress 06/01/18 to 05/31/22
Outputs
Target Audience:The target audience over the duration of the project has included the following: 1. One graduate student of color funded by this work 2. One post-doctoral student of color funded by this work 3. Five undergraduate students who have participated in this work, either voluntarily or for course credit. Of these, three were female and one was an African-American. 4. Approximately 30 students over two course offerings of ChE540: Coating Materials and Processing Applications, consisting of students from graduate and undergraduate levels across four different engineering departments, approximately 35% of whom were of color and approxmately 50% of whom were female. These students learned about coatings in general, and also participated in an experimental program within the course where they prepared thermal barrier coatings and measured hydrophobic improvements to the surface. 5. The broad scientific community working on thin coatings, food packaging and nanocellulose materials, including industrial and academic researchers. This work has been presented at various international conferences to disseminate the findings (e.g. NanoBoston, October 2021; AIChE, November 2021). Changes/Problems:A change in approach towards the end of this project was to introduce CaCl2 into the formulation, to assist with generating a network formation for CNC and/or CNF. Most of the work conducted earlier demonstrated vast improvements in thermal barrier, but preliminary SEM images indicated that a network was not found. CaCl2 is known to promote network formation, and hence was incorporated into later studies. Thermal barrier data tended to show some improvement with the CaCl2 present, and SEM images indicated a more robust network than had been observed previously. Additional work is needed to explore this change in more depth. Lack of student resouces over the Covid-19 period made it difficult to find sufficient help to explore this change and also to fully complete some agreed-upon tasks (see accomplishments), particularly after the post-doc and graduate student completed their work. Undergraduate volunteers were relied upon, but their own course schedules made it difficult for them to perform ongoing work on a continuous basis and hence much of the longer-term studies planned for environmental work did not get completed. The main objectives for this project, however, were largely realized. What opportunities for training and professional development has the project provided?Training Activities: 1. Seven students, ranging from undergraduate, Masters, and post-doctoral, participated in research activities related to this project, and hence developed experience and know-how on research skill in general as well as specific expertise in the area of thermal barrier coatings. These students learned how to develop experimental methods, conduct experiments carefully and meticulously, and analyze the resulting data. Graduate and post-doctoral students participated in more in-depth analysis of the data, and learned how to collate all the information into research presentations, posters, and publications. 2. Approximately 30 students participated in learning some of the methodology and protocols developed in this work during participation in a graduate-level course ChE540: Coating Materials and Process Applications. These students learned more generally about various coating components and their role in influencing bulk properties once coated onto a substrate. Professional Development: 1. In addition to the conference presentations already listed in 'major activities', the Masters student participated in departmental seminars each semester during while he was working on this project. 2. The PI also presented this work at the University of Alabama during as an invited guest speaker to the chemical engineering department (Fall 2021). 3. The PI and co-PI presented updates on this project at two NIFA grantees meetings, disseminating the knowledge to other grantees. How have the results been disseminated to communities of interest?Throughout the duration of this project, results have been disseminated to scientific communities via external conferences, publications, and internal university events such as summer REUs (Research Experiences for Undergraduates). With regard to communities who are not usually aware of such research activities, an article was published in the monthly engineering newsletter featuring the PI's undergraduate team at the time, and another article describing this project in general terms was published in the annual 'Ole Miss Engineer', to reach the broader audience. Additionally, the PI was a guest lecturer to a Liberal Arts Course (LIBA150), a course teaching basic chemistry to non-STEM students. During this lecture, the PI provided an overview of paper packaging and outlined some key features of packages to protect food, including the type of research that is being undertaken to further improve their functionality. Unfortunately the impacts of Covid-19 have limited the PIs and research team from participating in outreach events at nearby high schools where they could describe their work on a more general basis. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
IMPACT STATEMENT: This project sought to develop a coating on paper substrates using cellulosic biowaste to improve thermal, moisture, and mechanical properties. Its intended application is in the area of food packaging, specifically in transportation of goods and assisting in food redistribution efforts to areas of need while reducing food waste. PROJECT-RELATED ACCOMPLISHMENTS: The goal of this project is: "Exploit the unique properties of cellulose nanocrystal (CNC) and cellulose nanofiber (CNF) aerogels in the development of multifunctional coatings onto cellulose substrates". Objective 1: Incorporate in-house prepared CNC and CNF into standard paper coating formulations, to study the physiciochemical properties of the resulting precursor suspension. 1. Major activities completed / experiments conducted: Physicochemical properties of the precursor suspension (coating formulation) included a) viscosity measurements of coating formulations with CNC and CNF additives; b) dynamic light scattering (DLS) of dilute suspensions of individual coating components in DI water and CaCO3-saturated water; and c) laser scattering PSD measurements of dilute suspensions of individual coating components in 0.5 wt% CaCl2-water. 2. Data collected: Complex viscosity vs angular frequency of 2% CNC coating formulations (pH 7, 9) and 2% CNF coating formulations (pH 7, 9) using a cone and plate rheometer at Mississippi State University (MSU). DLS measurements included zeta potential and hydrodynamic diameter for dilute suspensions of CNC, CNF, dispersant, and latex in DI water and CaCO3-saturated water (pH 7, 8, 9); as well as dilute mixture suspensions of CNC+Latex+dispersant and CNF+Latex+dispersant in CaCO3-saturated water (pH 9). Measurements conducted on a Malvern Zetasizer Nano ZS (Malvern Instruments, UK). PSD measurements were conducted on a Horiba Laser Scattering PSD analyzer (Model: LA-960V2), and included dilute suspensions of CNC, CNF, CaCO3 and latex in 0.5 wt% CaCl2-water (pH 9); and dilute mixture suspensions of CNC+Latex+dispersant and CNF+Latex+dispersant in 0.5 wt% CaCl2-water (pH 9). 3. Summary statistics and discussion of results: Viscosity results: shear-thinning behavior of all formulations identified; formulations with CNF resulted in higher viscosities at low angular frequencies at pH 9. Zeta Potential and hydrodynamic diameter results: stable dispersions were created between pH 7-9 for all components except CNF, with ZP > 30 mV . Stable CNF dispersions were possible only at pH 9. Dilute suspensions involving all coating components were also found to result in stable dispersions. Hydrodynamic diameters of latex and dispersant were unaffected by the presence of CaCO3, but were reduced for CNC and CNF, indicating increased attractive forces between the nanoparticles as a consequence of added ions. Particle Size Distribution results: All individual components prepared in CaCl2-water resulted in much larger PSD (between 17 - 30 micron, except dispersant which was around 2 micron). CaCl2 assists in creating a network with CNC and/or CNF, and these results confirm that larger dispersions were formed. 4. Key outcomes or other accomplishments realized: Change in knowledge: Publications and conference presentations have resulted from this work. Change in action: 37 students have been directly impacted by this research work, and have been given tangible opportunity to adopt new and improved research skills via their participation in the project. Change in condition: not yet observed, however the change in knowledge has provided a good grounding for future technology transfer in food packaging operations. Objective 2: Generate multifunctionality of paper coatings with respect to superhydophobicity, thermal resistance and mechanical properties utilizing unique nano-additives and process variables to tune these properties. 1. Major activities completed / experiments conducted: Paper coatings were prepared with CNC and CNF additives, and the following bulk properties were investigated: a) thermal barrier properties; b) dynamic mechanic analysis; c) hydrophobicity of resulting coatings; and d) thermal conductivity of coatings and formulations. 2. Data collected: Preparation of coated papers with CNC and CNF additives: countless samples were prepared for bulk property analysis, and included air-drying and more rapid oven drying methods. Also, a small number of samples with 0.5 wt% CaCl2 were also prepared. Thermal barrier properties: Delta T measurements (temperature change across a coated sample) were taken on coated paper samples containing 2% CNC, 2% CNF; combinations of CNC/CNF additives introduced into coating formulations; formulations with CaCl2. DMA analysis: Performed on coated paper samples containing 2% CNC, 2% CNF; combinations of CNC/CNF additives introduced into coating formulations; formulations with CaCl2. Hydrophobicity of coatings: Contact Angle measurements were taken before and after thermal barrier treatments on coated paper samples containing 2% CNC, 2% CNF; combinations of CNC/CNF additives introduced into coating formulations; formulations with CaCl2. Thermal conductivity of coatings: 2% CNC additives in coated paper were sent off for thermal barrier testing. A modeling study was performed to predict the thermal conductivity of coating formulations containing 2% CNC and 2% CNF. LAAMPS software was used, along with a PCFF force field. 3. Summary statistics and discussion of results: Thermal barrier properties: Coating preparations with either CNC or CNF greatly enhanced the thermal barrier compared to 'baseline coatings' (no additive), irrespective of whether samples were air- or oven-dried. Air-dried samples averaged an additional delta T of 25 +/- 6C, while oven-dried samples recorded a delta T of 33 +/- 6C (compared with the baseline delta T). Additives introduced into the formulation in combination (CNC/CNF) showed improved thermal barrier, but generally the additives performed better when used individually. Delta T measurements on samples prepared with 0.5 wt% CaCl2 showed a small improvement in this value. DMA analysis: Addition of CNC and/or CNF improved the resistance to deformation, and indicated slightly higher dissipative energy due to positional movement of the additives within the coating. In general, a strengthened material was created. DMA results with samples prepared using CaCl2 showed no change in storage and loss moduli after 3 weeks for CNF, but increased for CNC additives. Hydrophobicity of coatings: Contact angle data generally showed a small increase after thermal barrier testing, but none of the coatings prepared promoted superhydrophobicity of the coatings. Presence of CaCl2 tended to promote a slightly higher CA, likely due to the better network formation and hence rougher surface of the coating. Thermal conductivity of the coatings: Experimental measurements of 2% CNC additive in a coated sample showed approx. a 30% reduction in thermal conductivity compared with the baseline-coated sample. Numerical modeling of coatings with 2% CNC and 2% CNF additives predicted a conductivity in a similar order of magnitude to that measured, and included variations of porosity within the coating. 4. Key outcomes or other accomplishments realized: As in point 4 for Objective 1. Discussion of Stated Goals not yet met: Both objectives were broadly met, although the superhydrophobicity of the coatings was not fully realized. While an increase in hydrophobicity was observed, explicit hydrophobic additives would need to be included in the formulation to further promote superhydrophobicity. Additionally, a longer-term environmental study of the optimized coating's performance was incomplete (only a three-week study was possible).
Publications
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2021
Citation:
Hutton-Prager, B. and Urena-Benavides, E. "Investigation of Cellulose Nanocrystals (CNC) and Cellulose Nanofibers (CNF) as Thermal Barrier and Strengthening Agents in Pigment-Based Paper Coatings. Nano Boston 2021, Oct 18-20 (Session: Nano Engineering & Nanomaterials for Energy & Environment)
- Type:
Journal Articles
Status:
Published
Year Published:
2021
Citation:
Hutton-Prager, B., Urena-Benavides, E., Parajuli, S., Adenekan, K. (2021) Cellulose Nanocrystals (CNC) and Cellulose Nanofibers (CNF) as Thermal Barrier and Strengthening Agents in Paper Coatings. Journal of Coatings Technology and Research, October. https://doi.org/10.1007/s11998-021-00538-1
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2021
Citation:
Mansourian-Tabaei, M, Asiaee, A, Hutton-Prager, B, and Nouranian, S. (2021). Thermal Barrier Coatings for Cellulose Substrates: A Designed Molecular
Simulation Study of the Effects of Nanoparticles and Porosity on Thermal
Diffusivity, The 2021 Annual Meeting of the American Institute of Chemical
Engineers (AIChE), Boston, MA, United States, November 7-11.
|
Progress 06/01/20 to 05/31/21
Outputs
Target Audience:The target audiences of our work this past year have included the following: 1. Two undergraduate female students during the Spring semester, as volunteers in the lab. One of these is an African-American student. 2. One undergraduate female student over summer, who participated in a REU (Research Experience for Undergraduates), entitled "Snazzy Surfaces for Students". This student intends to continue her work in the following year. 3. One graduate male student of color partly funded by this work. 4. One post-doctorate male student of color, as a volunteer during Summer 2020. Changes/Problems:Although several laboratories reopened in a workable manner despite covid restrictions, loss of funds during the initial closures and more recently a lack of researchers to work on this project has slowed its progress rather dramatically. Most original goals will be addressed by the end of this next reporting period, however, it fully depends on the time requirements of several undergraduate students, who will be doing the bulk of this work voluntarily. In terms of approach, addition of calcium chloride was not initially in the plan, however lack of network formation of the CNC and CNF when in the coating formulation has led us to look at other alternatives. This line of investigation has therefore been added to the program to promote thermal barrier formation. Additionally, the thermal conductivity trials have been more difficult to implement experimentally due to unavailable equipment in another lab that we were initially relying on, and we are attempting to make up this shortfall by investigating this aspect via theoretical modeling. This work is being conducted by graduate student Hanif Mansourian, who is due to complete his studies by year-end. What opportunities for training and professional development has the project provided?This project has enabled two undergraduate students to learn about research as volunteers during Spring 2021 (Clarie Calicdan and Alexis Kimpel). Additionally, another undergraduate student, Vy Dao, participated in a Summer REU and worked on this project, progressing several of its goals. In terms of training and professional development, the REU student particularly benefited greatly from her experience as she not only participated in the research itself, but attended weekly research meetings on 'how to do research' as well as listening to guest speakers discuss their work. Some of the 'how to' meetings included: a) how to analyze data; b) how to prepare a research poster; c) life of a graduate student; d) how to search for literature. The REU management team took several surveys and asked for frequent feedback, and initial results look very positive, with most REU students thoroughly enjoying their experiences and attracting them into research careers long-term. How have the results been disseminated to communities of interest?Results collected from the previous year have now been published in the Journal of Coatings Technology and Research, and this information is available in the 'Products' section of the annual progress report. Vy Dao also prepared a student poster and disseminated this work during the REU poster session across campus. Results from the published work has been accepted for presentation at NanoBoston 2021 (October 18-20) where the results will be disseminated to a wider audience. What do you plan to do during the next reporting period to accomplish the goals?During the next reporting period, we hope to complete the following tasks: * Environmental studies of coatings, extended to a 3 month period. This will involve repeat measurements of thermal barrier, CA, and storage/loss moduli, to see how these coatings fair over a longer time period. * Progress the work with calcium chloride additive. Preliminary studies show that it assists with the formation of a network and improves the CA. We need to investigate this more thoroughly with laser scattering techniques and SEM images to assess improvements to the network formation, as well as testing how this translates into improved thermal barrier. * Explore the thermal conductivity of these coatings, either theoretically or experimentally. It is hoped that REU student Vy Dao will be in a position to complete this remaining work.
Impacts
What was accomplished under these goals?
IMPACT STATEMENT: This project seeks to develop a coating on paper substrates using cellulosic bio-waste to improve thermal, moisture and mechanical properties. Its intended application is in the area of food packaging, specifically in transportation of goods and assisting in food redistribution efforts to reduce food waste. Experiments conducted by post-doctoral researcher Dr. Kola Adenekan towards the end of the previous reporting period were analyzed and written up into a research publication in this reporting year (detailed in 'Products'). Work performed on the precursor suspension in this reporting period by post-doctoral student Dr. Sanjiv Parajuli added critical learning to the knowledge-base. Undergraduate student Vy Dao participated in a REU to progress this work further in the areas of a) additives to the coating formulation to further enhance a microporous network between the CNC and CNF; and b) beginning the environmental trials of the prepared coatings. In summary, key results included identifying pH conditions that resulted in stable dispersions of coating components within the formulation prior to coating; optimizing the drying conditions of the coated paper to maximize the thermal barrier achieved; identifying which coating formulations gave the best thermal barrier; understanding the mechanical properties of the coated paper; gaining some initial insights into the effects of calcium chloride additive for improving aerogel networks and improved hydrophobicity; and finally identifying robustness of coating after three weeks of storage at refrigeration conditions. PROJECT-RELATED ACCOMPLISHMENTS The goal of this project is: "to exploit the unique properties of cellulose nanocrystal (CNC) and cellulose nanofiber (CNF) aerogels in the development of multifunctional coatings onto cellulose substrates". Objective 1: Incorporate in-house prepared CNC and CNF into standard paper coating formulations, to study the physicochemical properties of the resulting precursor suspension. 1. Major activities completed / experiments conducted: Zeta Potential (ZP) and Dynamic Light Scattering (DLS) studies were conducted on dilute suspensions of each coating component in DI water, and in DI water saturated with calcium carbonate ions. These coating components included latex binder, dispersant, CNC and CNF. Combinations of latex, dispersant, CNC; and latex, dispersant, CNF; were also mixed with DI water saturated with calcium carbonate ions to assess the effects all components together. These latter experiments mimicked a 'dilute version' of the concentrated suspensions used for the coating formulation. 2. Data collected: The ZP values measure the charge surrounding the colloids, and give an indication of stability of the resulting colloidal suspension. Stability is assumed if ZP > 30 mV. Hydrodynamic diameter, Dh, is measured using DLS, and this value indicates the diameter of the resulting colloids in suspension. Colloids formed that are too large may sediment out of 'solution', leaving smaller values of Dh that are measured. 3. Summary statistics and discussion of results: Stable dispersions of each coating component (binder, dispersant, CNC, CNF) could be created in water and water saturated with calcium carbonate ions across pH 7 - 9 except for CNF, which needed higher pH values to improve its stability. Calcium carbonate ions affected the hydrodynamic diameter of the dispersions containing CNC and CNF, indicating chemical interactions between these components. These effects were not observed with latex and dispersant components. 4. Key outcomes or other accomplishments realized: pH 9 is considered optimal to provide stable dispersions for CNF-based coatings, and was chosen for all coatings, given that the other components were relatively independent of pH. The calcium ions appear to interact with the nanoparticles (NP), and may contribute to creation of larger colloids that sediment out of 'solution'. However, presence of the latex binder and dispersant appear to reduce this possibility of sedimentation. Objective 2: Generate multifunctionality of paper coatings with respect to superhydrophobicity, thermal resistance and mechanical properties utilizing unique nano-additives and process variables to tune these properties. 1. Major activities completed / experiments conducted: Data analysis of thermal barrier and mechanical property trials conducted in the previous year was performed. Experiments conducted included introducing 0.5 wt% calcium chloride into the coating formulation with CNC and CNF, testing the resulting thermal barrier and hydrophobic performance; and preparing 2% CNC and 2% CNF calcium carbonate-based coatings to perform environmental trials to test their robustness with time. 2. Data collected: For the calcium chloride addition experiments, the 'delta T' was collected across each prepared coated paper, which is the temperature difference on the surface and underside of the coated paper. This is compared across different coatings, and higher delta T means a better thermal barrier. Also, the contact angle (CA) was measured before and after applying thermal load to these samples. For the environmental trials, thermal barrier performance (delta T) and mechanical property performance (storage and loss moduli under a temperature gradient) were measured at 0 and 3 weeks. 3. Summary statistics and discussion of results: Analysis of the thermal barrier trials and mechanical properties resulted in the following key conclusions: * CNC and/or CNF nanoparticles (NP) both contributed greatly to the improvement in thermal barrier when coated along with the remaining coating components onto paper substrates, as judged by measuring the delta T across the coated substrate. There was no significant difference between the performance of either NP, including whether or not they were combined within the same coating formulation or used individually. *Drying of the coatings showed that a higher rate of drying (oven drying for 4 h, at a rate of 25 degC/h) resulted in an additional 33 +/- 6 degC delta T, above that already obtained with a baseline coating (i.e. no CNC or CNF additive). Air-dried samples at approximately 1 degC/h resulted in an additional 25 +/- 6 degC of delta T. * Given that these coated papers are to be used in applications such as food packaging, the mechanical properties were also investigated, and both NP (tested together and individually) contributed to improved resistance to deformation (higher storage modulus). They also both contributed to a slightly higher loss modulus due to positional movement of the long-chain molecules within the coating, but reduced tan delta values (ratio between loss:storage modulus) indicated a strengthened material. Initial results from the experimental work completed are: * Small improvements in thermal barrier were obtained with the introduction of 0.5 wt% calcium chloride, particularly those prepared with CNF (approx. and additional 5 degC). * The CA after thermal treatment had increased to close to 150 degrees - the value for superhydrophobicity - with the CNF coatings, and approximately 125 degrees with the CNC coatings. * Environmental studies show that after three weeks, the delta T improved for both CNC and CNF-based coatings (11 and 7 deg C respectively); while storage and loss moduli values were maintained. Work is continuing in this area. 4. Key outcomes or other accomplishments realized: A research paper was published from the analysis of work conducted in the previous reporting period (see 'Products' section). Key conclusions as explained above in point 3 now provide a firm basis upon which to develop a coating for packaging applications, and a final task is to complete the environmental studies to confirm its robustness.
Publications
- Type:
Journal Articles
Status:
Awaiting Publication
Year Published:
2021
Citation:
Hutton-Prager, B., Urena-Benavides, E., Parajuli, S., Adenekan, K. Cellulose Nanocrystals (CNC) and Cellulose Nanofibers (CNF) as Thermal Barrier and Strengthening Agents in Paper Coatings. Journal of Coatings Technology and Research. Accepted June, 2021.
|
Progress 06/01/19 to 05/31/20
Outputs
Target Audience:The target audiences of our work this past year have included the following: 1. One graduate male student of color funded by this work; 2. One undergraduate student who assisted in the progress of this project, for course credit (ChE330). This student is a female African American; 3. One African male post-doctoral student who was employed in most of 2020 to progress this project and complete intermediate goals. Changes/Problems:One of the major hindrances in the past 12 months was the extreme slowing of the project by the graduate student due to personal health issues. This student was removed from the project in January, and a post-doc hired to get the project back on track. While Dr. Adenekan has done an excellent job in getting this project back on track, his progress has also been majorly hindered by the effects of the pandemic, with many laboratories closed. Most of the results that have been achieved appear to be giving the approximate expected results and are allowing the project to continue. Unfortunately however, the time line is significantly expanding due to these two main reasons (health issues of graduate student; global pandemic). What opportunities for training and professional development has the project provided?Dr. Kola Adenekan was hired on a short-term contract to progress this project after graduate student, Anas Al-Abri, assigned to this work was unable to continue due to ongoing health issues. As a result, the PDs were able to provide additional training to Dr. Adenekan in his first post-doctoral position, and he in turn provided key mentoring to an undergraduate student working directly with him, as well as a graduate student working on a similar area. How have the results been disseminated to communities of interest?Unfortunately, due to the graduate student's health issues and then the influence of the global pandemic, there have been few opportunities to disseminate this work to communities of interest. However, since the hiring of Dr. Adenekan to the group and the progression of some of this work (with coronavirus restrictions still in place), sufficient data has been gained to input into larger grants for continuing work. While this is not disseminating the work in the true sense, it is the beginning of this process. One small grant is looking at extending the results of this work down to refrigerated coatings, in order to assist with specimen collection for coronavirus testing purposes. With the more recent and reliable data collected, the PDs hope to write this up into a publication in the near future. This work was to have been presented at the Nanotechnology conference in June, which was unfortunately cancelled due to the pandemic. What do you plan to do during the next reporting period to accomplish the goals?Due in part to the closure of many laboratories with the onset of the pandemic, the plan for future work is a little unclear. The remaining work as per our original plan is as follows: Repeat the DLS and ZP work to get repeatable and reliable results, at the optimized conditions for thermal barrier work, in order to help explain the nature of the precursor formulation and the colloidal stability. Complete SEM imaging when this laboratory reopens. Determine surface porosity of the coatings from SEM images and ImagePro analysis. Introduce AKD or other hydrophobic additive into the coating formulation to further improve hydrophobicity of the coating. Perform thermal barrier trials under different humidity conditions, and attempt to determine preliminary values for the thermal conductivity. This work will be conducted mostly by undergraduate research students, as Dr. Adenekan's appointment will end shortly. There is another graduate student working on modeling of thermal barrier coatings, who may be able to take on some of this work as well, and at least lead the project for the undergraduate student. Unfortunately there has been considerable funds lost in the past half-year (Mar - Jul) with regard to still paying stipends to Dr. Adenekan with slower progress from the pandemic. Ideally, if some of these funds could be recouped once laboratories reopen, we would be in a better position to hire a researcher for a short period of time to make up this shortfall.
Impacts
What was accomplished under these goals?
IMPACT STATEMENT: This projects seeks to develop a coating on paper substrates using cellulosic bio-waste to improve thermal, moisture and mechanical properties. Its intended application is in the area of food packaging, specifically in transportation of goods and assisting in food redistribution efforts to reduce food waste. Post-doctoral researcher Dr. Kola Adenekan has conducted thermal barrier, contact angle (CA), morphological, and mechanical strength studies on coated papers, while creating a new formulation from a standard coating using cellulose nanocrystals (CNC) and cellulose nanofibers (CNF). Both are known to have excellent strength and thermal barrier properties. Key results indicate a measured temperature difference across a coated paper sample under applied thermal load of up to 30oC beyond that of a standard paper coating; maintenance of hydrophobic conditions on the surface to 126o; pH adjustment of the formulation to promote aggregation and network formation of CNC within the formulation; and a substantially higher strength coated paper with the introduction of CNF to the formulation. PROJECT-RELATED ACCOMPLISHMENTS: The goal of this project is: "to exploit the unique properties of cellulose nanocrystal (CNC) and cellulose nanofiber (CNF) aerogels in the development of multifunctional coatings onto cellulose substrates". Objective 1: Incorporate in-house prepared CNC and CNF into standard paper coating formulations, to study the physicochemical properties of the resulting precursor suspension. 1. Major activities completed / experiments conducted: Viscosity measurements of 2% CNC and 2% CNF formulations were taken on a cone-and-plate rheometer at Mississippi State University (MSU). 2. Data collected: Complex viscosity vs angular frequency of 2% CNC coating formulations (pH = 7 and 9) and 2% CNF coating formulations (pH = 7 and 9). 3. Summary statistics and discussion of results: The viscosity measurements were in the linear viscoelastic regime of the coating formulations, and showed shear thinning behavior for all formulations (typical behavior of coating formulations). The pH 9 formulations demonstrated higher viscosity across angular frequencies between 0.1 - 10 Hz compared with pH 7 preparations, and formulations with CNF had a higher viscosity than those with CNC at pH 9. At pH 7, this result was reversed, and need to be confirmed with more reliable ZP and DLS results, originally conducted in the previous year. 4. Key outcomes or other accomplishments realized: Higher starting viscosities are preferable due to shear thinning that occurs at the application nip or blade. These studies indicate that pH 9 formulations are a better choice from a runnability perspective. Objective 2: Generate multifunctionality of paper coatings with respect to superhydrophobicity, thermal resistance and mechanical properties utilizing unique nano-additives and process variables to tune these properties. 1. Major activities completed / experiments conducted: Thermal barrier tests confirmed with optimized 2% CNC in the coating formulation. Optimum quantity of CNF determined in the coating formulation, and also the optimum combination of CNC/CNF in the coating formulation, as judged by thermal barrier testing. Investigation of acetone drying conditions vs air drying conditions. CA studies conducted at optimal formulation conditions for both CNC and CNF, at pH 9 and overnight air drying. Morphological studies of the prepared samples performed using a scanning electron microscope (SEM). Dynamic mechanical analysis (DMA) testing on optimized coating formulations done to assess mechanical strength. 2. Data collected: Temperature profiles across coated substrates under different conditions (including pH and drying regimes). CA measurements of coatings before and after thermal applied loads, and also development of Zisman plots. SEM micrographs of selected coated substrates. DMA data to characterize the mechanical strength of the papers, both before and after heat treatment, to see the effects of thermally applied loads on mechanical strength. 3. Summary statistics and discussion of results: 2% CNC was the optimized concentration, with a thermal barrier of 44 ± 1 and 53 ± 12 oC under air drying conditions with the pH adjusted to 7 and 9, respectively. 2% CNF was the optimized concentration, with a thermal barrier of 20 ± 2 and 46 ± 4 oC under air drying conditions with the pH adjusted to 7 and 9, respectively. The baseline coating at the same conditions was 22 ± 8 and 24 ± 8 oC for pH 7 and 9 respectively, showing that the presence of CNC and CNF improve the barrier by approx. 22 - 29 oC over a variety of conditions, when the coating formulation is adjusted to pH 9. Acetone drying was considerably worse than air drying due to interaction of acetone with latex binder, causing some of the coating to be removed from the substrate. Air drying was chosen for subsequent drying methods. Work investigating combined CNC/CNF ratios in the coating formulation is still in progress, with repeatable results but not yet optimized thermal barriers. CA studies show that the mean CA before and after heat application for 2% CNC and 2% CNF formulations are all approximately 126 ± 6 o. The only anomaly of this work is the baseline post heat, which had reduced to 116 ± 2, indicating that CNC and CNF assist in maintaining the hydrophobicity of the surface even after applied heat. Morphological studies using the SEM for CNC, CNF, and baseline coatings generally showed: enhanced binder spreading over the pigment with heat; more aggregation of CNC when prepared with pH 9 formulations; better combinations of CNF with binder than with CNC. DMA studies showed that baseline and 2% CNC coatings have similar strength before and after thermally applied loads. 2% CNF coatings showed more than double the values of maximum storage modulus, and more than triple the values of maximum loss modulus for post-heat conditions compared with pre-heat conditions. The post-heat condition is also considerably higher than baseline and 2% CNC coatings, indicating the added strength that CNF typically brings to composite materials. Coatings prepared with 1%CNC:1%CNF were improved from coatings with just 2% CNC added. An increase in storage modulus generally indicates an increase in cross-linking between the bonds of chemical components, so it is possible that there is enhanced strength between the coating and substrate in these instances. An increase in the loss modulus indicates more liquid-like or viscous behavior; however, the tan delta for all samples was very low, indicating that the solid-like or elastic properties were dominant regardless of coating formulation being considered. 4. Key outcomes or other accomplishments realized: Consistent thermal barrier results achieved with 2% CNC and 2% CNF formulations, providing an additional temperature difference across a coated substrate (compared with the baseline) of 29 and 22oC, respectively. Air-drying methods of the coating are far more efficient than acetone-drying methods. CA studies show that the hydrophobicity of the coatings can be maintained even after thermally applied loads when CNC or CNF are added to the formulation. Morphological studies indicate that aggregation of the CNC occurs at higher pH, tentatively confirmed by the better thermal barrier at pH 9 compared with pH 7. Thermal treatment appears promote better interaction between binder and pigment. Plain paper (without coating) was affected by thermal loads in terms of a reduced mechanical performance, but coated papers were relatively similar pre- and post-heat, and less strong than uncoated paper. However, when 2% CNF was added to the coating, a dramatic increase in the storage modulus of the material was observed post-heat, in keeping with strength-enhancing properties of CNF commonly cited.
Publications
|
Progress 06/01/18 to 05/31/19
Outputs
Target Audience:The target audiences of our work this past year have included the following: 1. one graduate student of color funded by this work; 2. two undergraduate students who have assisted in the progress of this project; 3. 17 students (mix of graduate and undergraduate from 4 different engineering departments, 35% of color) who participated in ENGR597(12) Coatings and Materials Processing Applications course, also conducting an experimental program within the course related to this thermal barrier and hydrophobic coating project; 4. The Pulp and Paper Industry in Columbus, MS, to source pulp in order to prepare CNC and CNF in-house. The University of Maine have also been contacted directly to purchase pre-made CNC/CNF for comparisons. 5. The broad scientific community working on thin coatings, food packaging and nanocellulose materials, including industrial and academic researchers. Changes/Problems:One of the major delays experienced in the past year has been the lack of availability of the SEM. We have purchased a new SEM from a MRI-NSF, and it has taken approximately 4 months longer to successfully install than anticipated. Commissioning has just been completed, and training is under way with the new instrument. While this issue has now been resolved, unfortunately some of the earlier work which required the SEM has been delayed. Another potential delay for the coming year is the use of the Tenney environmental chamber, which appears to be having some issues at holding humidity at higher temperatures. We may be able to do the testing at lower temperatures however. We were also hoping to use this and/or some other equipment in chemistry to measure the thermal conductivity, and this may impact progress somewhat. However, thermal conductivity of just the optimized coated samples can be sent away for external testing via contacts of the PD in Canada. At this stage, there are no significant deviations from the research goals, and results so far are encouraging, and going approximately as planned. The schedule may be pushed back a little due to the above delays identified. What opportunities for training and professional development has the project provided?During the first year of this seed grant, there were many opportunities for training activities. A new graduate student, Anas Al-Abri, joined the thermal barrier team with support of this grant, and was initially trained in several experimental techniques required for the project by senior PhD graduate students. He learned how to prepare CNC and CNF from wood pulp supplied by Columbus, MS; prepared coating formulations and applied them onto paper substrates; and developed expertise in several measurement techniques (CA; DMA; rheological techniques; AFM, Zeta potential; and DLS). Undergraduate student Brandon Knight has participated consistently within Dr. Prager's research team over several years, and has also learned new research techniques. Both students have been mentored by Drs Prager and Urena-Benavides in guidance and planning of conducting research, and have progressed well. Additionally, Dr. Prager in Spring 2019 ran a coating materials processes and applications course (ENGR597(12)) in which 17 students participated in learning in depth the multi-facets of coating formulations. An experimental component planned for all students included preparing the thermal barrier coatings in this project, and learning how to image the coating and take contact angle measurements. Professional development activities by the PD (Dr. Prager) in this past year in direct relation to this grant included SEM training of the new instrument recently installed in the Pharmacy Department, and preparation of a publication which included the thermal barrier formulation developments. Both professors attended the recent NIFA conference in Nashville, TN (May 2019), and benefited greatly from the collaborations generated and useful discussions. How have the results been disseminated to communities of interest?Some of the early results of this work were published in Cellulose, 2019 (https://doi.org/10.1007/s10570-019-02426-9), thereby disseminating scientific information regarding the potential of the thermal barrier coatings being studied. At a more general level for outreach activities, two articles were published within the University of Mississippi. The first was in the monthly engineering newsletter (2018, https://news.olemiss.edu/engineering-research-group-developing-coatings-sturdier-packaging/), where Dr. Prager's undergraduate research team was featured. This made mention of the thermal barrier project along with her other work. The second was in the annual 'Ole Miss Engineer' magazine (2019, https://www.engineering.olemiss.edu/news/olemiss_engineer/2018-19/olemissengineer2018-19.pdf), where this project was specifically discussed, with initial results being cited but at a more general level. Both these efforts have assisted public understanding of an 'every day topic' of food packaging, and the complex science behind preparation of such packages. What do you plan to do during the next reporting period to accomplish the goals?During the next reporting period, the following key experimental programs will be conducted: Finalize the Zeta Potential measurement work to identify the actual pH that is required for optimal aggregation of individual components. Confirm this also with DLS and other measurements as necessary. Using the final, optimized formulation conditions, prepare coated substrates and explore different drying regimes to promote aerogel formation of the CNC or CNF. Confirm this structure with SEM imaging. Conduct thermal barrier trials with the optimized formulation and drying regime, and explore different times for thermal loads (possibly a range of different heat loads as well). Compare the before and after samples from these trials with Zisman plots; CA measurements; SEM imaging; and mechanical testing (tensile testing; indentation tests; DMA). Conduct longer-term environmental tests of the optimized formulations under varying humidity conditions prior to mechanical testing, and also do some preliminary trials with these coated samples by subjecting them to food-loads, such as proteins or carbohydrates, to assess their performance with that. Note - there is likely to be a 'back-and-forth' between many of these tasks as information from one task informs that of another.
Impacts
What was accomplished under these goals?
IMPACT STATEMENT: While food packaging has improved the storage and quality of packaged foods dramatically, environmental conditions such as excessive heat and moisture during transportation can lead to a loss of mechanical integrity of the package, compromising the food contained within. This project seeks to address this issue by developing a coating on paper substrates that has enhanced thermal and moisture properties, and also retains (or even enhances) its mechanical strength. During the first year of this grant, graduate student Anas Al-Abri took fundamental measurements of each component in the coating formulation to assess their aggregation ability. pH values were identified in which an aggregated formulation could form, hence optimizing the formulation for subsequent coating onto the paper substrates. The temperature difference across the coated substrate was measured to assess thermal barrier performance. Coatings prepared with 2% cellulose nanocrystal (CNC) additive provided the best barrier to date, with an additional 28.3oC temperature difference beyond what the standard coating (without additive) was able to provide. Hydrophobic performance was tested on the same formulation, and an increase in contact angle (CA) of 23.2o was observed after heat treatment. There was no thermal degradation occurring during the thermal barrier tests, indicating that a change in morphology due to the applied heat was promoting both a better thermal barrier and a more hydrophobic surface. In the broader context, the longer term impacts of this work include the following: Utilizing cellulosic waste from agricultural industries to extract CNC and cellulose nanofiber (CNF) for further use. Incorporating CNC and/or CNF into standard coating formulations for paper substrates already used by the paper industry. Development of enhanced food packaging with much better thermal barrier and moisture properties that can protect the foodstuffs in the event of extreme environmental stress. Less food wastage for the general population, and enhanced potential to deliver and store foods successfully in harsh environmental conditions. The goal of this project is: "to exploit the unique properties of cellulose nanocrystal (CNC) and cellulose nanofiber (CNF) aerogels in the development of multifunctional coatings onto cellulose substrates". Objective 1: Incorporate in-house prepared CNC and CNF into standard paper coating formulations, to study the physicochemical properties of the resulting precursor suspension. 1) Major experiments completed / experiments conducted: Dilute solutions of each component present in the coating formulation (CNC, CNF, latex binder, dispersant) were prepared in DI water and saturated calcium carbonate water at pH of 8 and 9, to determine the zeta potential and hydrodynamic diameter of each component. Viscosity measurements of the full formulation were taken using a cone and plate rheometer. CNC and CNF were prepared using wood pulp from Columbus, MS, and were characterized using AFM measurements. 2) Data collected: mV readings for Zeta Potential; Hydrodynamic diameter from DLS measurements; Viscosity and shear stress with increasing and decreasing shear rate values for rheological measurements; Length and height values of the isolated CNC from AFM characterization. 3) Summary statistics and discussion of results: The Zeta Potential measurements showed negative mV readings, indicating that a stable colloidal dispersion is possible when dispersed in water and low ionic strength solutions. The hydrodynamic diameter for each of the individual components was only moderately affected by the presence of saturated calcium carbonate; in general, a small increase was observed. This indicates that the components can successfully aggregate in the coating formulation. The viscosity measurements are ongoing, as problems were identified with the viscometer. An alternate viscometer has been sourced, and measurements will continue shortly. The results of this work are expected to show different rheological behavior of the formulations when prepared at optimal pH conditions and with each of the additives. This will assist in determining the best composition to apply the coating. The AFM measurements for CNC, isolated via acid hydrolysis, showed an average length of 128 ± 43 nm and heights of 6.4 ± 1.8 nm. CNF, prepared by mechanical grinding, resulted in widths of 50 nm and several microns long. 4) Key outcomes or other accomplishments realized: The key outcomes of this work have helped identify the pH conditions needed to prepare the formulations, and enabled methodology development for investigating precursor suspensions prior to coating application and performance studies. Similar experiments will be done at additional pH to fully complete this work. Objective 2: Generate multifunctionality of paper coatings with respect to superhydrophobicity, thermal resistance and mechanical properties utilizing unique nano-additives and process variables to tune these properties. 1) Major experiments completed / experiments conducted: Coating formulations with CNC and CNF prepared and coated onto paper substrates Optimal quantity of CNC or CNF added to the standard formulation determined, as judged via thermal barrier tests. Zisman plots and CA measurements of coated surfaces with optimized CNC quantity. Thermal Gravimetric Analysis (TGA) conducted on dried coating formulation with optimized CNC quantity. 2) Data collected: Microscopic imaging of prepared coated samples Plots of temperature difference across coated paper sample vs concentration of CNC or CNF additive in the formulation. Zisman plots using ethanol/water solutions to determine critical surface energy of the coated samples, before and after heat treatment. CA measurements using sessile drop methods with DI water, before to after heat treatment. Weight loss % from TGA of dried coating formulation with increasing temperature, and constant temperature with increasing time. 3) Summary statistics and discussion of results: Coating techniques using the ChemInstruments coater were developed to uniformly apply coating formulations to paper substrates. Microscope imaging was used to determine uniformity of the prepared samples. Thermal barrier trials measured the temperature difference across coated samples with respect to % CNC or CNF addition. The optimum for CNC was 2% (based on pigment added), and CNC participates in phonon scattering at the interface to reduce the thermal conductivity (Diaz et al, 2014). Filling in of substrate pores by CNC fragments helps create a microporous surface that also enhances thermal barrier and hydrophobic properties. Zisman plots for coating formulations with 2% CNC showed a reduction in critical surface energy of 13 mN/m as a result of thermal barrier testing. TGA results confirmed minimal degradation over similar times and thermal loads; therefore, development of microporosity and microroughness during heat treatment are likely responsible. This will be confirmed with SEM studies over the summer period. The sessile CA measurements showed an increase of over 20o as a result of the thermal testing, leading to a final CA of 120.5 ± 8.1o. With continued optimization of the formulation as outlined in objective 1, this value can be further increased. Different drying regimes of the coating, and longer times during the thermal barrier testing will be explored to determine their influence, if any, on hydrophobic development. 4) Key outcomes or other accomplishments realized: Although this work is not yet complete, the key outcomes to date include identifying optimal quantities of both additives with respect to thermal performance; an important lack of thermal degradation confirmed during thermal tests; and a modest improvement in the hydrophobicity of the surface. This work will further be refined to continue to determine key outcomes for this project.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2019
Citation:
Hutton-Prager, B., Khan, M. M., Gentry, C., Knight, C. B., Al-Abri, A. K. A. (2019) "Thermal barrier enhancement of calcium carbonate coatings with nanoparticle additives, and their effect on hydrophobicity", Cellulose 26: 4685-4880. https://doi.org/10.1007/s10570-019-02426-9
- Type:
Other
Status:
Published
Year Published:
2019
Citation:
Prager, B. (2019). "Stop the Heat!", Ole Miss Engineer, p. 27, 40. https://www.engineering.olemiss.edu/news/olemiss_engineer/2018-19/olemissengineer2018-19.pdf
- Type:
Other
Status:
Published
Year Published:
2018
Citation:
Smith, E. B. (2018). "Engineering Research Group Developing Coatings for Sturdier Packaging", Engineering E-newsletter. https://news.olemiss.edu/engineering-research-group-developing-coatings-sturdier-packaging/
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