Welcome to the Bortner Research Group

 

Dr. Michael Bortner

Assistant Professor
Department of Chemical Engineering,
Virginia Tech
2270 Kraft Drive, Suite 1303
(540) 231-4213
(540) 231-5022 (fax)
Email: mbortner@vt.edu


 

Research

Modeling of FDM Failure Scenarios

Since the debut of 3D printing as a means of prototyping materials, there has been a huge push for the implementation of additive manufacturing on an industrial scale. This allows for the printing of unique and dynamic designs in real time, eliminating the need for costly molds and specialized manufacturing processes. Even though large strides have been made to strengthen additive manufacturing capabilities, further investigation is still needed to understand the fundamental processes to enable implementation of next generation materials and technologies.

Development of processes to successfully print next generation (composite) thermoplastic materials for FDM printing requires a fundamental understanding of the relationship between printhead/nozzle design and the combined interaction of the physical and mechanical properties with the rheology of the printed material. We are implementing continuum based models to successfully predict failure modes of a newly designed material, and enable sequential design of the printer system to successfully print these next generation polymers (composites) that would otherwise fail to print in currently available system designs.

Mechanically Adaptive Materials

Our group is developing mechanically adaptable, implantable material technologies for personalized medicine using additive manufacturing processes. Additive manufacturing affords custom shaping and sizing for individual patient needs, and also facilitates unique architectures to control mechanical properties in 1, 2 or 3 dimensions. By fabricating rigid materials that are mechanically adaptive to the body's environment, we can tailor devices for ease of implantation and subsequent adaptation to the body's natural environment. We are currently conducting tests on the physical properties of different polymer-based materials in both wet and dry conditions.


Figure 1. Flow Profile in Fused Filament Modeling Nozzle

Particle-Matrix Interface Characterization

Polymer nanocomposite materials have significant potential for applications that require light-weight structural components. During nanocomposite processing, interactions between the nanoparticle filler and the polymer matrix are governed by several factors including specific surface interactions, and mass transport due to localized concentration gradients that arise from differences in chemistry and corresponding surface energy. In the case of thermoset nanocomposites, the kinetics of the curing reaction substantially impact the nature of the interphase region between the polymer and nanoparticles and, by extension, the final material properties. Practically, issues such as particulate flocculation, agglomeration, and the macroscopic distribution within the composite also substantially influence bulk structure property relationships.

Unfortunately, the nature of the interphase region between nanoparticle fillers and the bulk matrix in polymer nanocomposites is still not well understood, particularly in thermosetting systems. Current composite development approaches rely on educated compositional guesses to meet targeted properties and performance, and on corresponding compositional studies to phenomenologically model and optimize each individual nanocomposite system.

Our group is working to characterize the interfacial area between particle and matrix to gain a better understanding of the interphase gradient, and ultimately, to build a model for predicting the interactions at the interphase regions for different polymer nanocomposite systems. The goal is to streamline optimal system design for future. We are studying a model thermosetting composite system to establish baseline comparisons for comparison to a broad literature base. We are implementing unique characterization strategies to explore the morphology and thermodynamic state of the interphase region.


Figure 2. Thermosetting Nanocomposite Interphase Gradient

Cellulose Nanocrystals

The introduction of cellulose wood fibers in nanocomposite materials is a substantial discovery in biorenewable nanotechnology. Cellulose nanocrystals (CNCs), with a width of 5-10 nm, are particularly advantageous given their natural abundance, low weight, and unique structural and biodegradable properties. They are most commonly used in industrial processes to increase the strength of composite materials. CNCs have been studied for quite some time, but there is still much to be understood when it comes to attaining proper dispersion/suspension within composites as well as conditions in which to maximize production yield. We are currently using two statistical models, CCD and BBD, to investigate the synthesis of cellulose nanocrystals through both sulfuric acid hydrolysis and ammonium persulfate direct carboxylation. Through this research, we aim to determine and maximize the production yield of cellulose nanocrystals on an industrial scale, combined with a tailored approach for obtaining desired functionality for specific applications.

Nucleation of Cellulose Nanocrystal Films

Our group is currently investigating methods to nucleate and grow silver nanoparticles on the surface of cellulose nanocrystals, with the ultimate goal of developing unique 3-D percolating polymer composite networks for transparent, conductive electrodes. We have demonstrated the potential to successfully nucleate and grow silver nanoparticles on CNC templates in the form of a stable, optically clear/transparent aqueous colloid. Our approach is unique compared to traditional metallic NP growth schemes, in that we simultaneously take advantage of reagent limiting reactions and competing reaction kinetics. Our current efforts are focused on controlling NP growth for targeted specific size/morphology, concentration, and nanoparticle population density on the CNC template. Additionally, we are implementing unique methodologies for translating this colloid precursor into a uniform 3-D (electrically) percolating network.


Figure 3. AFM of Directly Carboxylated Cellulose Nanocrystals


 

Publications

  • S. Dong, M.J. Bortner, and M. Roman, "Analysis of the Sulfuric Acid Hydrolysis of Wood Pulp for Cellulose Nanocrystal Production: A Central Composite Design Study". Ind. Crop Prod., (2016) in press.

  • Quigley, J.P., M. Bortner, K. Herrington and D. Baird, "Benign Reduction of Carbon Nanotube Agglomerates Using a Supercritical Carbon Dioxide Process". J. Appl. Phys. A, 117, 1003 (2014)

  • C. Chen, M. Bortner, J.P. Quigley, and D.G. Baird, "Using Supercritical Carbon Dioxide in Preparing Carbon Nanotube Nanocomposite: Improved Dispersion and Mechanical Properties", Polymer Composites, 33, 6, 1033 (2012)

  • T. Mukundan, V.A. Bhanu, K.B. Wiles, H. Johnson, M. Bortner, D.G. Baird, A.K. Naskar, A.A. Ogale, D.D. Edie and J.E. McGrath, "A photocrosslinkable melt processible acrylonitrile terpolymer as carbon fiber precursor", Polymer, 47, 11, 4163 (2006)

  • Bortner, M.J., and D.G. Baird, "Absorption of CO2 and Subsequent Viscosity Reduction of an Acrylonitrile Copolymer", Polymer, 45, 10, 3399 (2004)

  • Bortner, M.J., V.A. Bhanu, J.E. McGrath, and D.G. Baird, "Absorption of CO2 in High Acrylonitrile Content Copolymers: Dependence on Acrylonitrile Content", Polymer, 45, 10, 3413 (2004)

  • Bortner, M.J., V.A. Bhanu, J.E. McGrath, and D.G. Baird, "Shear Rheological Properties of Acrylic Copolymers and Terpolymers Suitable for Potentially Melt Processable Carbon Fiber Precursors", Journal of Applied Polymer Science, 93, 6, 2856 (2004)

  • Bortner, M.J., P.J. Doerpinghaus, and D.G. Baird, "Effects of Sparse Long Chain Branching on the Spinning Stability of LLDPEs", International Polymer Processing, 19, 3, 236 (2004)

  • Bhanu, V.A., P. Rangarajan, K. Wiles, M.J. Bortner, M. Sankarpandian, D. Godshall, T.E. Glass, A.K. Banthia, J. Yang, G. Wilkes, D. Baird, and J.E. McGrath, "Synthesis and Characterization of Acrylonitrile Methyl Acrylate Statistical Copolymers as Melt Processable Carbon Fiber Precursors", Polymer, 43, 18, 4841 (2002)

  • Bhanu, V.A., K.B. Wiles, M.J. Bortner, D. Godshall, T.E. Glass, D.G. Baird, G.L. Wilkes, and J.E. McGrath, "Synthesis and Rheological Study of Polyacrylonitrile Copolymer Carbon Fiber Precursors Using Cost Effective Water Based Synthesis Routes", Polymer Preprints, 43, 1 (2002)


 

Contact

Polymer and Composite Materials Lab

2270 Kraft Drive, Suite 1303
Blacksburg, Virginia 24060
Telephone (540) 231-4213 Fax: (540) 231-5022
Email: mbortner@vt.edu

Department of Chemical Engineering

Suite 245 Goodwin Hall, 635 Prices Fork Road
Blacksburg, Virginia 24061.
Telephone: (540) 231-6631 Fax: (540) 231-5022