About

Donald Baird is a Professor Emeritus in the Department of Chemical Engineering at Virginia Tech. He holds a Ph.D. from the University of Wisconsin obtained in 1974, an M.S. from Michigan State University in 1971, and a B.S. from Michigan State University in 1969. His research interests include polymer processing, specifically the design and simulation of polymer processing and rheology, as well as composite materials and processing. Additionally, he focuses on polymeric materials and their properties. His work involves understanding and advancing the processing and application of polymeric and composite materials, contributing to the field through research and education at Virginia Tech.

Research topics

• Composite material
• Materials science
• Chemical engineering

Selected publications

• Highly stiff and strong fiber reinforced core‐shell composites for <scp>3D</scp> printing

  Polymer Composites · 2024-12-18 · 1 citations

  articleOpen accessSenior authorCorresponding

  Abstract A novel core‐shell continuous polymeric fiber reinforced composite with excellent mechanical performance was prepared using a dual‐extrusion process. Continuous pumping of a thermotropic liquid crystalline polymer (TLCP) into polyamide 6 (PA6) via dual‐extrusion equipped with a core‐shell circular die enabled the generation of continuous fiber reinforced composite filaments with core‐shell structure. Microscopic analysis confirmed the composition of the composite and the core‐shell macroscopic morphology where the TLCP core was surrounded by a polyamide shell. The core‐shell structure exhibited a strong weld‐strength of 3D printed parts with improved tensile properties which was attributed to the strong inter‐diffusion and entanglement of polyamide chains across the printed layers. The average tensile strength of 3D printed core‐shell TLCP‐polyamide material was measured to be 132.7 MPa, which is an improvement of about 50% compared to its “sea‐island” TLCP‐polyamide counterparts prepared using the same dual extrusion process with added static mixers. A comparison between the printed core‐shell 20 wt% TLCP‐PA6 and continuous traditional glass‐fiber reinforced composite revealed that the printed core‐shell 20 wt% TLCP‐PA6 exhibited a tensile modulus (~12 GPa) approximately 300% higher than that of its 20 wt% glass‐fiber/polyamide counterpart. The continuous TLCP composite filament can be printed with a generic extrusion‐based 3D printer without requiring any modification, and the presence of continuous TLCP fibers in the filament core has no adverse effect on the printability. Notably, sharp turns (e.g., 180° changes in printing direction) can be achieved during the printing without creating fiber‐less regions in the printed parts which overcomes one of the major limitations of printing continuous glass or carbon‐fiber reinforced composites. By leveraging the core‐shell morphology with TLCP's lightweight and reinforcement properties, we successfully fabricated high strength and stiff additively manufactured parts with enhanced interlayer bonding. Highlights Prepared core‐shell fiber reinforced polyamide using dual‐extrusion technology. 3D printed continuous fiber reinforced composite filaments. Significant improvements in mechanical properties of polyamide. Higher modulus than conventional 3D printed glass fiber composite.

  PublisherOA PDFDOI

• The rheology of ultra-high molecular weight poly(ethylene oxide) dispersed in a low molecular weight carrier

  Physics of Fluids · 2022-02-01 · 5 citations

  articleOpen accessSenior author

  Gel spinning is the industrial method of choice for combining hydrophilic ultra-high molecular weight (UHMW) polymer resins with a hydrophobic support polymer to produce composite filaments for cytapheresis. Cytapheresis is a medical technique for removal of leukocytes from blood. Gel spinning is used to avoid high melt viscosity and thermal sensitivity of UHMW resins and the high melt temperature of the substrate resin but requires the recovery of toxic solvents. The UHMW resin is used because it forms a stable gel phase in the presence of water; a lower molecular weight resin (LMW) simply dissolves. UHMW and LMW resins were both poly(ethylene oxide) (PEO) and the substrate was polyarylsulfone (PAS). The literature indicated PEO undergoes non-oxidative thermal degradation above 200 °C and PAS is processed up to 350 °C. Dynamic oscillatory shear rheometry was used to study 0, 25, 40, 50, 60, and 75 wt. % UHMW PEO in LMW PEO to take advantage of the sensitivity of viscosity to changes in molecular weight and material configuration, indicating degradation. Samples were exposed to 220 °C, 230 °C, 240 °C, 250 °C, 275 °C, and 300 °C temperatures for 5 min to explore conditions that could result in sample degradation. The viscosity decreased less with increasing UHMW PEO content for samples exposed to the same temperature and the viscosity decreased more with increasing exposure temperature for samples with the same UHMW PEO content. Parameters were regressed from observed data to predict the change in molecular weight via empiricisms relating the viscosity to molecular weight, shear rate, temperature, and time.

  PublisherOA PDFDOI

• The influence of processing conditions on tensile properties of wholly thermoplastic composites reinforced with nanotubes

  Polymer Composites · 2021-02-11 · 8 citations

  articleSenior authorCorresponding

  Abstract This paper is concerned with novel wholly thermoplastic composites (WTCs) reinforced with supercritical carbon dioxide‐aided exfoliated multi‐walled carbon nanotubes (MWCNTs) and the enhancement of mechanical properties. The bicomponent in situ injection molded plaques consist of polyamide 6 (PA6) and microfibers of thermotropic liquid crystalline polymer (TLCP) with miss‐matched melting temperature. Multiple mixing histories with MWCNTs and processing temperatures were studied and tested for minimizing matrix thermal degradation and maximizing tensile properties of the multi‐scale WTCs. The optimum in situ injection molding temperature was found at 300°C with melt blending nylon 6 matrix and exfoliated MWCNTs in advance. Exfoliated MWCNTs acted as bridging elements between the TLCP and the nylon 6 matrix, which lead to effective stress transfer from the nylon 6 matrix to the TLCP fibrils. Compared to the WTCs without MWCNTs reinforcement, tensile modulus and tensile strength in longitudinal and latitudinal directions were both improved. Furthermore, with the reinforcement of TLCP and exfoliated MWCNTs, the tensile modulus and tensile strength of nylon 6 were enhanced by 173% and 35% in the fluid flow direction, respectively. These experimental results for 20 wt% TLCP/PA6 were even better than the mechanical properties of 20 wt% carbon fiber (CF)/PA6 reported in the literature.

  PublisherDOI

• Thermotropic liquid crystalline polymer reinforced polypropylene composites enhanced with carbon nanotubes for use in fused filament fabrication

  Polymer Composites · 2021 · 28 citations

  Senior authorCorresponding
  • Materials science
  • Composite material

  Abstract The objective of this research was to enhance the mechanical properties of wholly thermoplastic composites (WTCs) used in fused filament fabrication (FFF). Multiscale thermoplastic composites, which were based on the use of polypropylene (PP) reinforced with thermotropic liquid crystalline polymer (TLCP) and carbon nanotubes (CNTs), were prepared by a method combining supercritical carbon dioxide (scCO 2 )‐aided exfoliation and dual‐extrusion technologies. Significant enhancement of tensile properties was observed by using 1 wt% exfoliated CNTs to reinforce WTCs consisting of PP with and without maleic anhydride‐grafted polypropylene (MAPP, 16 wt%). With 1 wt% CNTs and 16 wt% MAPP dual reinforcement, 20 wt% TLCP reinforced WTCs based on PP exhibited 265%, 274%, and 182% improvement in the tensile modulus of the filaments, laid up specimens in the concentric pattern, and laid up specimens in ±45° rectilinear pattern, respectively. For tensile strength, 1 wt% CNTs reinforcement combined with 16 wt% MAPP improved the 20 wt% TLCP reinforced WTC filaments, laid down parts in the concentric pattern, and ±45° rectilinear patterns by 73%, 53%, and 65%, respectively. The tensile modulus and strength of multiscale WTC based on MAPP/PP specimens laid down with a concentric pattern are higher than those reported for PP/40 wt% short carbon fiber and PP/48.5 wt% short glass fiber laid down specimens. The advanced tensile modulus properties of 1 wt% CNTs reinforced WTCs are competitive with 9 wt% continuous carbon fiber reinforced nylon composite materials in FFF. Scanning electron microscopy analysis showed extremely strong interfacial adhesion between the TLCP fibrils and the matrix in multiscale WTC filaments and laid down parts, compared to the WTCs with no CNTs reinforcement. The advanced interfacial adhesion between TLCP fibrils and matrix resulted in an enhancement in the tensile strength. The exfoliated CNTs were premixed with the matrix, but they were trapped at and aligned with TLCP fibrils, which may be the primary reason for tensile modulus enhancement.

  PublisherDOI

• Thermotropic liquid crystalline polymer reinforced polyamide composite for fused filament fabrication

  Additive manufacturing · 2021-03-02 · 24 citations

  articleSenior authorCorresponding
  PublisherDOI

• Generation of nylon copolymer reinforced with carbon nanotubes and thermotropic liquid crystalline polymers for use in fused filament fabrication

  Polymer Composites · 2021-06-02 · 21 citations

  articleSenior author

  Abstract Multiscale thermoplastic composites consisting of nylon copolymer (PAc) reinforced with thermotropic liquid crystalline polymer (TLCP) and carbon nanotubes (CNTs) were generated in the form of strands and then processed via fused filament fabrication (FFF). The tensile modulus and strength of the laid‐up strands were found to be similar to those reported for polymer reinforced with nearly continuous carbon fibers. In this paper, 1 wt% CNTs were discovered to significantly enhance tensile properties of a nylon copolymer (PAc) reinforced with 20, 30, and 40 wt% TLCP wholly thermoplastic composite (WTC). The WTC filaments were then laid down via fused filament fabrication (FFF). Based on the previous work carried out in our lab, 1 wt% CNTs were the crucial concentration to efficiently enhance carbon fiber (CF) reinforced multiscale composites. The deagglomerated CNT dispersion in the WTCs was accomplished by using supercritical carbon dioxide (scCO 2 ). The effects of TLCP concentration and printing patterns in the lay‐down processes were explored. The most improvement in tensile properties due to the 1 wt% addition of CNTs was observed to be for the 20 wt% TLCP/1 wt% CNTs/PAc samples. The resulting composite filaments exhibited 225% and 80% improvement in the tensile modulus and strength, respectively, compared to the wholly thermoplastic composites (WTCs) without CNTs. In addition, 40 wt% TLCP/1 wt% CNT/PAc 3D printed specimens with filaments laid parallel to the printing direction exhibited excellent tensile modulus and strength of 38.92 GPa and 127.16 MPa, respectively. The measured tensile modulus of 40 wt% TLCP reinforced WTC is even higher than the reported 69 wt% long glass fiber (LGF) or 26 wt% long carbon fiber (LCF) reinforced nylon in fused filament fabrication with the same printing pattern.

  PublisherDOI

• Development of Recyclable and High-Performance In Situ Hybrid TLCP/Glass Fiber Composites

  Journal of Composites Science · 2020 · 22 citations

  Senior authorCorresponding
  • Materials science
  • Composite material

  By combining the concepts of in situ thermotropic liquid crystalline polymer (TLCP) composites and conventional fiber composites, a recyclable and high-performance in situ hybrid polypropylene-based composite was successfully developed. The recycled hybrid composite was prepared by injection molding and grinding processes. Rheological and thermal analyses were utilized to optimize the processing temperature of the injection molding process to reduce the melt viscosity and minimize the degradation of polypropylene. The ideal temperature for blending the hybrid composite was found to be 305 °C. The influence of mechanical recycling on the different combinations of TLCP and glass fiber composites was analyzed. When the weight fraction ratio of TLCP to glass fiber was 2 to 1, the hybrid composite exhibited better processability, improved tensile performance, lower mechanical anisotropy, and greater recyclability compared to the polypropylene reinforced by either glass fiber or TLCP alone.

  PublisherOA PDFDOI

• Macroscopic fiber orientation model evaluation for concentrated short fiber reinforced polymers in comparison to experimental data

  Polymer Composites · 2020-03-10 · 17 citations

  articleSenior author

  Abstract Advanced macroscopic fiber orientation models depend on a variety of phenomenological parameters. The aim of this work is to identify a fiber orientation model for concentrated short fiber reinforced polymers, which depends on a minimum number of parameters. A sliding plate experiment with repeatable initial conditions and a couette experiment, to cover high strains, are used to define an experimental validation curve. The major fiber orientation models (Folgar and Tucker, nematic, reduced strain closure [RSC], anisotropic rotary diffusion, ARD‐RSC) are fitted to the validation curve. Since a slow evolution can be observed, the RSC model is necessary to fit the measured fiber orientation evolution. The dependency of the RSC model on the initial fiber orientation state and the influence of closure approximations are evaluated. Two validation cases show that the obtained parameters give good results in shear dominant parts, but are not able to predict fiber orientation in other flow regimes accurately.

  PublisherDOI

• Efficient parameter identification for macroscopic fiber orientation models with experimental data and a mechanistic fiber simulation

  AIP conference proceedings · 2020-01-01 · 6 citations

  articleOpen accessSenior author

  Advanced macroscopic fiber orientation models depend on a variety of phenomenological parameters. The prediction quality is closely related to the choice of those parameters. Therefore, the aim of this research is to propose an efficient method for parameter identification. First, a macroscopic fiber orientation model for concentrated short fiber-reinforced polymers with a minimum number of parameters has to be identified. To define the macroscopic model a comparison with experimental data is used. A sliding-plate experiment with repeatable initial conditions is conducted for obtaining fiber orientation evolution under controlled shear and temperature conditions. Then the fiber orientation models are fitted to the experimental validation curve. Since the experimental curve generation for parameter fitting is time and cost consuming, a more efficient method is exploited: a mechanistic direct fiber simulation. The simulation can then be used to generate fiber orientation curves for varying physical descriptors (fiber length, fiber length distribution, volume fraction, viscosity, shear rate).

  PublisherOA PDFDOI

• Comparing fiber orientation evolution between startup of shear and nonlubricated squeeze flow

  Polymer Composites · 2020-09-23 · 5 citations

  articleSenior author

  Abstract Light weighting has become an integral part of vehicle design. This strategy makes use of fiber‐reinforced thermoplastics, which can be injection molded into complex shapes. Composite design work requires knowledge of the orientation state throughout a part to predict properties like stiffness and strength. Although evolution models for the orientation state have been developed, each requires empirical parameters, and no standard method for obtaining these exists. This work continues efforts to find such a test, particularly for long (average length &gt; 1 mm) glass fiber composites. Here, a polypropylene loaded with 30, 40, and, 50 wt% long glass fiber is subjected to startup of shear and nonlubricated squeeze flow (NLSF). The orientation evolution was reported for both flows and an attempt was made at fitting several orientation models to the data. The measured orientation evolution from startup of shear was slower than expected, and this slower evolution appears to result from the combination of the initial orientation state and fiber concentration. On the other hand, the measured orientation profile from NLSF was found to be essentially independent of fiber concentration. However, the NLSF orientation profile could not be replicated with a single set of parameters. Rather, shear‐like parameters made reasonable predictions in shear‐dominated regions, and extension‐like parameters made reasonable predictions in extension‐dominated areas, in concordance with results from short glass fiber composites.

  PublisherDOI

Recent grants

• Simulation of Injection Molding of Thermoplastics Reinforced with Fibers and Nano-Particles

  NSF · $360k · 2005–2009

• Simulation of Molding of Long Fiber Thermoplastic Composites

  NSF · $415k · 2009–2013

• Materials World Network: Molecular Engineering of Polymers for Processing Performance and Properties

  NSF · $480k · 2006–2009

Frequent coauthors

• Peter Wapperom

  Virginia Tech

  24 shared

• Gregorio M. Vélez-García

  Oak Ridge National Laboratory

  15 shared

• Garth L. Wilkes

  14 shared

• Michael J. Bortner

  Virginia Tech

  12 shared

• Aaron P. R. Eberle

  ExxonMobil (United States)

  10 shared

• Jier Y. Han

  Virginia Tech

  8 shared

• Tianran Chen

  8 shared

• James E. McGrath

  8 shared