Progress 07/01/17 to 06/30/22
Outputs
Target Audience:This research is focused on the development of new structural materials that exploit the unique properties of cellulose nanofibrils. Thus, the target audience of this research is the materials community and the cellulose/paper/pulp community. Work from this project has been presented/published in the materials research community. A goal of publishing this work in the materials community is to share the promise of natural and sustainable materials with a broader audience. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Our collaborative team was led by PD Prof. Kevin Turner at the University of Pennsylvania (Penn) and by co-PDs Dr. Craig Clemons and John Considine at the USDA, US Forest Service, Forest Products Laboratory (FPL). The PDs and co-PDs collectively co-advised and shared knowledge with several students that performed research as part of this project. This provided a rich environment for student training and gave the students the opportunity to develop technical skills in several areas, including materials, nanocellulose, mechanics, and polymer processing. Over the course of the project, three undergraduate students and two PhD students were involved in the project. Two of the undergraduates were students at the University of Wisconsin-Madison (majoring in Chemical Engineering) and did research on this project working at FPL with co-PD Clemons. The third undergraduate was an undergraduate student at University of Pennsylvania and worked on the project in the lab of PD Turner. Both PhD students (majoring in Mechanical Engineering and Applied Mechanics) were based at the University of Pennsylvania. The primary PhD student on the project completed his degree in 2022 and is now employed as a research engineer in Industry at 3M. How have the results been disseminated to communities of interest?Two journal papers on this work have been published as noted in the Products section. We also presented the work at conferences as noted in the products section. Three more journal papers based on work in this project will be completed and submitted in the future. What do you plan to do during the next reporting period to accomplish the goals?The project is complete.
Impacts
What was accomplished under these goals?
During the fifth and final year of the project, our team completed the project. Work towards Goals 1 and 3 was completed in earlier years and described in previous reports. On Goal 2, we switched to an alternate approach to realize CNF reinforced films earlier in the project (see year 3, 4 reports for description and rationale of alternate film approach) because of challenges encountered in making the PMMA-CNF films. In the alternate approach, a cellulose network is first formed and then polymer is infiltrated/coated into/onto the network (this is in contrast to the previous approach of mixing CNF and polymer and then extruding). The new approach was described in a previous progress report. Briefly, the strategy is to start with a microscale cellulose network (e.g. filter paper), selectively infiltrate CNFs into this microscale network by coating with an aqueous CNF solution and allowing it to dry, and then coating this cellulose composite with a polymer. The combination of microscale and nanocellulose fibers lead to a hierarchical material with improved strength and toughness. Furthermore, the CNF solution can be deposited locally (i.e. printed) on the microscale cellulose network sheets in specific patterns to add heterogeneity at a larger length scale (~mm) to further engineer the mechanical properties. During the past year, we refined this approach and extensively investigated (1) the infiltration of CNFs into microscale cellulose networks and (2) how mm-scale regions of infiltrated CNFs can be used to engineer mechanical properties (strength and toughness). Uniform infiltration of the CNF was demonstrated to increase the toughness of the sheets by approximately a factor of 2 and the strength by approximately a factor of 2.25. The degree of infiltration and properties of the CNF-infiltrated regions as a function of process were also characterized. Through printing the CNF solution, mm-scale patterns of infiltrated material were created in the sheets, and it was shown that the toughness could be further enhanced through this patterning. Two papers describing the properties of these CNF-infiltrated materials and their characterization are currently under preparation.
Publications
- Type:
Theses/Dissertations
Status:
Published
Year Published:
2022
Citation:
Gnana Saurya Vankayalapati, "Enhancing strength and toughness via reinforcement with nanocellulose fibers," PhD Thesis University of Pennsylvania (2022).
- Type:
Journal Articles
Status:
Other
Year Published:
2023
Citation:
Gnana Saurya Vankayalapati, Adam Taylor, Michal Budzik and Kevin T. Turner, "Hinged Rigid Beam Test for Evaluation of Fracture Toughness of Thin Sheet and 2D Materials" to be submitted to Experimental Mechanics (2023)
- Type:
Journal Articles
Status:
Other
Year Published:
2023
Citation:
Lisa M. Lallo, Gnana Saurya Vankayalapati, Sumukh S. Pande, John M. Considine, and Kevin T. Turner, "Orientation and mechanical properties of printed cellulose nanofibril thin sheets" to be submitted to Cellulose (2023).
- Type:
Journal Articles
Status:
Other
Year Published:
2023
Citation:
Gnana Saurya Vankayalapati and Kevin T. Turner, "Hierarchical Architected Cellulose Sheets with Improved Toughness using Elastic Heterogeneity," to be submitted to ACS Applied Materials and Interfaces (2023).
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Progress 07/01/20 to 06/30/21
Outputs
Target Audience:This research is focused on the development of new structural materials that exploit the unique properties of cellulose nanofibrils. Thus, the target audience of this research is the materials community and the cellulose/paper/pulp community. Work from this project has been presented/published in the materials research community. A goal of publishing this work in the materials community is to share the promise of natural and sustainable materials with a broader audience. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Our collaborative team is led by PD Prof. Kevin Turner at the University of Pennsylvania (Penn) and by co-PDs Dr. Craig Clemons and John Considine at the USDA, US Forest Service, Forest Products Laboratory (FPL). The PDs and co-PDs collectively co-advise and share knowledge with several students that are performing research as part of this project. This provides a rich environment for student training and has given the students the opportunity to develop technical skills in several areas, including materials, nanocellulose, mechanics, and polymer processing. To date, three undergraduate students and two PhD students have been involved in the project. Two of the undergraduates were students at the University of Wisconsin-Madison (majoring in Chemical Engineering) and did research on this project working at FPL with co-PD Clemons. The third undergraduate was an undergraduate student at University of Pennsylvania and worked on the project in the lab of PD Turner. Both PhD students (majoring in Mechanical Engineering and Applied Mechanics) were based at the University of Pennsylvania. The project is currently in an NCE and during the past reporting period, there is one active PhD student on the project. How have the results been disseminated to communities of interest?Two journal papers on this work have been published as noted in the Products section. We also gave a conference presentation on the work in 2019. The pandemic has limited other conference opportunities, but we plan to present this work at future conferences as in-perosn meetings return. What do you plan to do during the next reporting period to accomplish the goals?During the final year of the project, we will: (1) Aim to demonstrate robust PMMA-CNF laminates via the alternate approach described above. This will include fabrication of the laminates and mechanical characterization. (2) Complete our work on infiltrated CNF films through material fabrication and mechanical testing. We expect at least two more journal publications on work in this project to submitted by the end of the project.
Impacts
What was accomplished under these goals?
During the fourth year of the project, our team pursued three primary efforts: (1) We finalized and published the paper on the PMMA-CNF fiber work (goal 1) in ACS Applied Polymer Materials. (2) We investigated PMMA-CNF laminates as part of goal 3 . (3) We continued to explore and alternate approach to producing films/sheets of polymer reinforced by CNFs (see year 3 report for description of alternate film approach) (1) CNF-PMMA fibers: We finalized and published the paper on CNF-PMMA fibers. The work is published as: G.S. Vankayalapati, E. Kaplan, L.M. Lallo, N. Victor, C.M. Clemons, J.M. Considine, and K.T. Turner, "Toughening poly(methyl methacrylate) via reinforcement with cellulose nanofibrils," ACS Applied Polymer Materials, 3, 6102-10 (2021). (2) CNF-PMMA laminates: As discussed in previous reports, an alternate composite material strategy to making a blend of CNF and PMMA is to create laminate structures consisting of alternating layers of CNFs and PMMA (goal 3 above). Laminate structures offer greater opportunity to design materials with specific mechanical responses and to incorporate larger amounts of CNF in the materials. As noted in previous reports, we had obtained encouraging results using silanes to functionalize the CNF and PMMA sheets in order to achieve bonding in the laminates. While the preliminary results were encouraging, the interfaces formed via the use of silanes proved to have poor stability over time. Thus, silane functionalization was ultimately deemed to not be a viable route to produce mechanically robust CNF laminates. Working with a collaborator in chemical engineering at U. Penn, we have developed an alternate approach to obtain interlaminar adhesion in CNF-PMMA laminates. In this new approach: (1) amination of PMMA is performed through the use of hexamethylene diamine to form -NH2 groups on the surface (2) A CNF gel is treated with a water-soluble EDC carbodiimide (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride). The aminated PMMA and EDC treated CNF are expected to bond when brought into contact and dried. Experiments to verify this approach are ongoing. In parallel with the effort to achieve good adhesion in laminates, we worked to develop a mechanical characterization technique (and associated computational modeling methods) that can be used to characterize the interlaminar toughness of CNF-PMMA laminates. The fracture specimen that was developed for this purpose is a double cantilever bean (DCB) geometry. To develop and demonstrate this DCB fracture technique, we applied the technique to characterize the interlaminar toughness of a larger-scale cellulose network material as a model system. This work was published as: R. Spiewak, G.S. Vankayalapati, J.M. Considine, K.T. Turner, and P.K. Purohit, "Humidity dependence of fracture toughness of cellulose fibrous networks," Engineering Fracture Mechanics, 264, 108330 (2022). https://doi.org/10.1016/j.engfracmech.2022.108330 (3) The second goal in the proposal is focused on preparation and characterization of PMMA-CNF films in which the CNFs are dispersed throughout a PMMA film. This is a 2-D analog to the 1-D fibers that were examined in #1 above. As described previously, initial work on PMMA-CNF films in this project showed that extruding PMMA-CNF films was challenging due to the thermal stability of the CNFs and the ability to achieve good dispersion. As a result, we modified our approach to realizing polymer-CNF films in goal 2 during the past reporting period and began to investigate an approach where a cellulose network is first formed and then polymer is infiltrated/coated into/onto the network (this is in contrast to the previous approach of mixing CNF and polymer and then extruding). The new approach was described in the previous progress report. During this current reporting period, we mechanically characterized composites in which CNFs were selectively infiltrated into a microscale cellulose network and demonstrated that strategic placement of CNFs within the films can lead to significant enhancement of fracture toughness. These microcellulose/CNF networks can subsequently be infiltrated with polymers. We also carried out computational modeling to understand the mechanics of these composite materials.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2021
Citation:
G.S. Vankayalapati, E. Kaplan, L.M. Lallo, N. Victor, C.M. Clemons, J.M. Considine, and K.T. Turner, Toughening poly(methyl methacrylate) via reinforcement with cellulose nanofibrils, ACS Applied Polymer Materials, 3, 6102-10 (2021). https://doi.org/10.1021/acsapm.1c00933
- Type:
Journal Articles
Status:
Published
Year Published:
2022
Citation:
R. Spiewak, G.S. Vankayalapati, J.M. Considine, K.T. Turner, and P.K. Purohit, Humidity dependence of fracture toughness of cellulose fibrous networks, Engineering Fracture Mechanics, 264, 108330 (2022). https://doi.org/10.1016/j.engfracmech.2022.108330
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Progress 07/01/19 to 06/30/20
Outputs
Target Audience:This research is focused on the development of new structural materials that exploit the unique properties of cellulose nanofibrils. Thus, the target audience of this research is the materials community and the cellulose/paper/pulp community. Work from this project has been presented/published in the materials research community. A goal of publishing this work in the materials community is to share the promise of natural and sustainable materials with a broader audience. Changes/Problems:Our original approach to fabricate films (goal 2 in the original proposal) did not work as anticipated. As a result, we developed an alternative approach to making polymer-CNF films. The problems with the original approach and the alternative approach that was developed are explained in the Accomplishments section (item #3) of this report. What opportunities for training and professional development has the project provided?Our collaborative team is led by PD Prof. Kevin Turner at the University of Pennsylvania (Penn) and by co-PDs Dr. Craig Clemons and John Considine at the USDA, US Forest Service, Forest Products Laboratory (FPL). The PDs and co-PDs collectively co-advise and share knowledge with several students that are performing research as part of this project. The PDs and co-PDs meet individually with students and the team also holds bi-weekly videoconferences. This provides a rich environment for student training and has given the students the opportunity to develop technical skills in several areas, including materials, nanocellulose, mechanics, and polymer processing. To date, three undergraduate students and two PhD students have been involved in the project. Two of the undergraduates were students at the University of Wisconsin-Madison (majoring in Chemical Engineering) and did research on this project working at FPL with co-PD Clemons. The third undergraduate was an undergraduate student at University of Pennsylvania and worked on the project in the lab of PD Turner. Both PhD students (majoring in Mechanical Engineering and Applied Mechanics) are based at the University of Pennsylvania and are doing research on this project in the lab of PD Turner. How have the results been disseminated to communities of interest?One of the PhD students gave an oral presentation on his work on the project at the Society for Experimental Mechanics Annual Meeting in June 2019. A journal paper summarizing our research on PMMA-CNF fibers is complete and we are working towards getting it through the peer-review process. What do you plan to do during the next reporting period to accomplish the goals?During year 4 of the project, we will continue working on the fabrication and characterization of PMMA-CNF laminates as noted above. We will characterize the interface toughness (i.e. adhesion) as a function of environmental conditions and the overall fracture resistance of the laminates. The experiments will be supported by computational modeling for materials design and understanding failure and energy dissipation mechanisms in PMMA-CNF composites. We will also continue investigating the synthesis and properties of polymer-CNF films as noted in #3 in the accomplishments section. This includes work to implement the polymer infiltration/coating process, computational modeling to design films that leverage the multiscale nature of the reinforcement, and mechanical characterization of the films.
Impacts
What was accomplished under these goals?
During the third year of the project, our team pursued two primary efforts: (1) We completed the paper on the PMMA-CNF fiber work, including a few additional experiments needed to complete the understanding presented in the paper. (2) We investigated the fabrication of PMMA-CNF laminates and characterized the mechanical properties using a silane chemistry at the interface. (3) We developed alternate approach to producing films/sheets of polymer reinforced by CNFs. (1) CNF-PMMA fibers: We completed the paper summarizing the PMMA-CNF fiber work and are currently working to get the paper published in a peer review journal. The paper is entitled "Toughening Poly(methyl methacrylate) via reinforcement with cellulose nanofibrils" and the abstract is given here: The incorporation of fibers into polymers is a well-known route for realizing composite materials with improved strength, stiffness, and toughness. Cellulose nanofibrils (CNFs) are a promising reinforcement due to their high aspect ratio, high specific stiffness and specific strength, transparency, and the fact they are derived from renewable and sustainable sources. Here, we demonstrate the application of CNFs for the reinforcement of continuous polymer fibers (filaments) to achieve a concurrent enhancement of strength, stiffness, and fracture toughness. Polymethylmethacrylate (PMMA)-CNF composite fibers with 0 to 3 wt. % CNFs were made by solvent blending and melt spinning/drawing techniques, resulting in fibers with diameters ranging between 200-300 micrometers. The processing route was developed to overcome challenges presented by the combination of high processing temperatures of PMMA and the low thermal stability of CNFs as well as formation of a percolated CNF networks and low volume fractions. Fourier transform infrared (FTIR) spectroscopy was used to understand the alignment of the CNFs in the fibers. The strength and Young's modulus of the fibers were characterized by tensile testing and the fracture toughness was measured via notched fibers tests. The addition of low weight fractions (<3%) of CNFs increased the Young's modulus by 35% and yield strength by 19% compared to neat PMMA fibers. Along with this increase in stiffness and strength, the results show that the incorporation of 1 wt. % CNF leads to a doubling of the fracture toughness. FTIR results and imaging of the fracture surfaces provide insight into the mechanisms of toughening. (2) CNF-PMMA laminates: An alternate composite material strategy to making a blend of CNF and PMMA is to create laminate structures consisting of alternating layers of CNFs and PMMA (goal 3 above). Laminate structures offer greater opportunity to design materials with specific mechanical responses and to incorporate larger amounts of CNF in the materials. We are following a general approach that consists of making neat films of CNFs (~55 micrometers in thickness) and laminating these films with PMMA sheets of similar thickness (~40-60 micrometers). The key challenge in this work is achieving good adhesion between the CNF and PMMA. During this reporting period, we developed an approach based on a silane chemistry to achieve good adhesion between CNF and PMMA. Specifically, the surface of the CNF film is functionalized with APTES and the surface of the PMMA is functionalized with GPTES. After the surfaces are functionalized, the CNF and PMMA interface are bonded by applying pressure (70 psi). Typically, we make three layer laminates consisting of two PMMA face sheets with a CNF layer in the middle. Bonding can be achieved at room temperature, but we are also investigating the effect of elevated temperature (e.g. 70 C) on the bond strength and time for bonding. Without the silanes, no measurable adhesion is measured if the PMMA-CNF interfaces are pressed at room or elevated temperature. With the silanes, the layers of the laminate remain adhered. The adhesion was quantified via double cantilever beam fracture tests. The interfaces with the highest adhesion strengths and toughnesses of >25 J/m^2, which is sufficiently high for use of the laminates in structural applications. In general, the adhesion increases with increased pressing time and higher adhesion can be achieved at shorter times by pressing at elevated temperature. The transport and migration of water near the CNF-PMMA interface is believed to play a major role in the temperature and time dependence of the adhesion strength. Other tests done during the reporting period show that the laminates retain transparency and that the CNF laminate has a Young's modulus that is 3.5x greater than pure PMMA. During the next reporting period, we characterize the mechanical properties of the laminates fully and also examine the environmental stability of the interface. We have also completed complementary computational modeling of the fracture process during this reporting period. (3) The second goal in the proposal is focused on preparation and characterization of PMMA-CNF films in which the CNFs are dispersed throughout a PMMA film. This is a 2-D analog to the 1-D fibers that were examined in #1 above. Initial work on PMMA-CNF films in this project showed that extruding PMMA-CNF films was challenging due to the thermal stability of the CNFs and the ability to achieve good dispersion. As a result, we modified our approach to realizing polymer-CNF films in objective 2 during this reporting period. Specifically, we began to investigate an approach where a cellulose network is first formed and then polymer is infiltrated/coated into/onto the network (this is in contrast to the previous approach of mixing CNF and polymer and then extruding). This modified approach offers the opportunity for better dispersion and higher volume fractions of CNFs. The challenge with this approach is that a cellulose network with porosity must be created and CNFs form dense films with little to no porosity. Thus, the approach we have adopted is to infiltrate CNFs into a porous network of microscale cellulose fibers. This multi-scale cellulose network can then be infiltrated or coated with polymers. The CNFs can be infiltrated in the microscale cellulose network locally to introduce property variation at larger length scales to further engineer the toughness. During this reporting period, we (1) developed this approach, (2) demonstrated infiltration of CNFs into the microscale cellulose networks, and (3) performed computational modeling to design these materials. While this approach to realizing composite films is a change from the original approach proposed, we believe this new approach will lead to materials with better properties and allow for the use of CNFs to toughen polymers, consistent with the original proposal goals.
Publications
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2019
Citation:
Gnana Saurya Vankayalapati, Sumukh S. Pande, Lisa M. Mariani,
John M. Considine, Craig M. Clemons, Kevin T. Turner, "Characterization of interface toughness of cellulose nanofibril and polymer composite laminates" presented at the 2019 Annual Meeting of the Society of Experimental Mechanics, June 2019
- Type:
Journal Articles
Status:
Other
Year Published:
2021
Citation:
Gnana Saurya Vankayalapati, Ethan Kaplan, Lisa M. Mariani, Nikhil Victor, Craig M. Clemons, John M. Considine, Kevin T. Turner, "Toughening Poly(methyl methacrylate) via reinforcement with cellulose nanofibrils" under revision 2021
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Progress 07/01/18 to 06/30/19
Outputs
Target Audience:This research is focused on the development of new structural materials that exploit the unique properties of cellulose nanofibrils. Thus, the target audience of this research is the materials community and the cellulose/paper/pulp community. Changes/Problems:No major changes, What opportunities for training and professional development has the project provided?Our collaborative team is led by PD Prof. Kevin Turner at the University of Pennsylvania (Penn) and by co-PDs Dr. Craig Clemons and John Considine at the USDA, US Forest Service, Forest Products Laboratory (FPL). The PDs and co-PDs collectively co-advise and share knowledge with several students that are performing research as part of this project. The PDs and co-PDs meet individually with students and the team also holds bi-weekly videoconferences. This provides a rich environment for student training and has given the students the opportunity to develop technical skills in several areas, including materials, nanocellulose, mechanics, and polymer processing. To date, three undergraduate students and two PhD students have been involved in the project. Two of the undergraduates were students at the University of Wisconsin-Madison (majoring in Chemical Engineering) and did research on this project working at FPL with co-PD Clemons. The third undergraduate was an undergraduate student at University of Pennsylvania and worked on the project in the lab of PD Turner. Both PhD students (majoring in Mechanical Engineering and Applied Mechanics) are based at the University of Pennsylvania and are doing research on this project in the lab of PD Turner. How have the results been disseminated to communities of interest?A poster on the work was presented at the Gordon Research Conference on Nanoscale Science and Engineering for Agriculture and Food Systems. One of the PhD students gave an oral presentation on his work on the project at the Society for Experimental Mechanics Annual Meeting in June 2019. A journal paper summarizing our research on PMMA-CNF fibers is in preparation and will be submitted in Fall 2019. What do you plan to do during the next reporting period to accomplish the goals?During year 3 of the project, we will continue working on the fabrication and characterization of PMMA-CNF laminates. This will include work to further improve and characterize the interface adhesion of PMMA-CNF layers and a detailed investigation of the mechanical properties of laminates, including fracture toughness and impact resistance. The experiments will be supported by computational modeling for materials design and understanding failure and energy dissipation mechanisms in PMMA-CNF composites.
Impacts
What was accomplished under these goals?
During the second year of the project, our team pursued two primary efforts: (1) We completed the experimental work on preparation and characterization of composite CNF-PMMA fibers that was started in year 1 and are currently writing a journal paper summarizing the results. (2) We investigated the fabrication of PMMA-CNF laminates and characterized the mechanical properties of the laminate interfaces. Specific accomplishments related to these goals are detailed below. (1) CNF-PMMA fibers: During the first year, we fabricated and characterized PMMA fibers reinforced with cellulose nanofibril (CNF) materials with volume fractions from 0.5 to 3%. These fibers were produced with melt spinning and drawing and the basic physical and mechanical properties of these fibers were characterized in year 1. In year 2, we did additional characterization of these fibers including fracture toughness testing and FTIR to characterize CNF dispersion/alignment. Fracture toughness testing on fibers is not standard and required the development of specialized techniques, including complementary mechanics modeling. Through the experimental work done in years 1 and 2, we have developed an understanding of the potential use of CNF as a reinforcement in PMMA. Through the addition of 1% CNF in PMMA, the Young's modulus was increased from 3.3 GPa to 4.2 GPa (28%) and the yield strength was increased from 77 MPa to 89 MPa (16%). By increasing the CNF content further to 3%, the modulus was increased to 4.5 GPa and the yield strength was increased 93 MPa. Fracture toughness, which is the key focus of this project showed an interesting trend with CNF content - the toughness increased with increasing CNF content up to 1% and then decreased at higher concentrations (2% and 3%). The fracturetoughness of neat PMMA was 0.8 MPa-m1/2 and that of PMMA with 1% CNF was 1.9 MPa-m1/2 (an increase of 137%). Thus, CNF reinforcement, even at low volume fractions of CNF, has been shown through this work to have a significant positive impact on improving fracture resistance of PMMA. This is consistent with the hypothesis presented in the original proposal that CNFs hold significant potential for toughening polymers. We are currently preparing a journal paper summarizing these results along with supporting measurements and models that give insight into the micromechanics of toughening with CNFs. (2) CNF-PMMA laminates: An alternate composite material strategy to making a blend of CNF and PMMA is to create laminate structures consisting of alternating layers of CNFs and PMMA. Laminate structures offer greater opportunity to design materials with specific mechanical responses and to incorporate larger amounts of CNF in the materials. We are following a general approach that consists of making neat films of CNFs (10-60 micrometers in thickness) and laminating these films with PMMA sheets of various thicknesses. The challenge in making laminates is achieving strong adhesion between the CNF film and PMMA. It is challenging because of a lack of specific bonding between CNF and PMMA and the high smoothness and low porosity of CNF films. Several approaches based on thermal processing were tried to realize adhesion in PMMA-CNF laminates, but they did not work. However, an alternative approach based on using silanes as coupling agents was developed and this has yielded promising results. Preliminary interface adhesion measurements using a fracture-based double cantilever measurement suggests that this bonding approach yields an interface toughness of 30-40 J/m2, which is quite high for the PMMA-CNF system. Ongoing work is focused on the continued development of the bonding process, fabrication of laminates, and characterization of the fracture toughness of the laminates.
Publications
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2019
Citation:
G.S Vankayalapati, S.S. Pande, L.M. Mariani, J.M. Considine, C.M. Clemons, K.T. Turner, "Preparation and characterization of cellulose nanofibril and polymer composite laminates," SEM Annual Conference 2019, Reno, NV.
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Progress 07/01/17 to 06/30/18
Outputs
Target Audience:This research is focused on the development of new structural materials that exploit the unique properties of cellulose nanofibrils. Thus, the target audience of this research is the materials community and the cellulose/paper/pulp community. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Our collaborative team is led by PD Prof. Kevin Turner at the University of Pennsylvania (Penn) and by co-PDs Dr. Craig Clemons and John Considine at the USDA, US Forest Service, Forest Products Laboratory (FPL). The PDs and co-PDs collectively co-advise and share knowledge with several students that are performing research as part of this project. The PDs and co-PDs meet individually with students and the team also holds bi-weekly videoconferences. This provides a rich environment for student training and has given the students the opportunity to develop technical skills in several areas, including materials, nanocellulose, mechanics, and polymer processing. To date, two undergraduate students and two PhD students have been involved in the project. Both undergraduates are students at the University of Wisconsin-Madison (majoring in Chemical Engineering) and did research on this project working at FPLS with co-PD Clemons. Both PhD students (majoring in Mechanical Engineering and Applied Mechanics) are based at the University of Pennsylvania and are doing research on this project in the lab of PD Turner. How have the results been disseminated to communities of interest?A poster on the work was presented at the Gordon Research Conference on Nanoscale Science and Engineering for Agriculture and Food Systems. Journal papers and other conference presentations summarizing the research results will be pursued in years 2 and 3 of the project. What do you plan to do during the next reporting period to accomplish the goals?During year 2 of the project, we will: (1) Complete the characterization of the PMMA/CNF composite fibers and finish the work on the fibers that was detailed in the proposal. (2) Fabricate and characterize the properties of PMMA/CNF films. This includes basic structural and mechanical characterization and will also pursue SEM-based in-situ mechanical tests to identify underlying toughening mechanisms. (3) Investigate different approaches for modifying CNFs and PMMA to achieve strong adhesion in laminates.
Impacts
What was accomplished under these goals?
During the first year the project, our team developed approaches to manufacture CNF-PMMA composites in fiber form and characterized the properties of these composite fibers. This involved development of techniques to combine CNFs (which are produced in an aqueous solution) with PMMA to obtain a blend that can be formed into composite fibers and sheets. The development of this process required some iteration, but an effective route consisting of solvent blending, melt spinning, and subsequent drawing was established to produce CNF-PMMA fibers with up to 3% CNF. We characterized composition, structure, and basic properties of the composite fibers using multiple techniques: polarized light microscopy, differential scanning calorimetry, and scanning electron microscopy. The mechanical properties of the fibers were characterized via tensile testing. Toughness is a key focus of this project, thus we worked to improve the fiber test methods to allow for measurement of toughness in addition to Young's modulus and yield strength. The fiber characterization efforts are ongoing, however the mechanical measurements performed to date show that incorporation of 3% CNF into PMMA leads to an increase in both the yield strength and toughness relative to pure PMMA. It is significant that both strength and toughness are increased as many approaches for manipulating polymer properties exhibit a tradeoff in strength and toughness; for example, drawing of neat PMMA fibers increases strength, but decreases ductility and toughness. We expect to complete the research on PMMA-CNF fibers during summer 2018. In addition to the fiber work described above, we have also performed initial work on fabricating composite films and laminates. The film work is a direct follow-on to the fiber work and leverages processing techniques developed for making fibers. Manufacturing laminates is fundamentally different from the fiber/film processing techniques and involves lamination of multiple sheets of neat PMMA and neat CNF. The neat CNF sheets are made by removing water from the solution to form CNF 'nanopapers'. The laminates provide a route to integrate larger volume fractions of CNFs into composites than blending approaches.
Publications
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