Engineering topics

Barnes, Sietske H.

Publications and source records attributed to Barnes, Sietske H..

4 records

DOE OSTI2019

An Ionomeric Renewable Thermoplastic from Lignin-Reinforced Rubber

An ionomeric, leathery thermoplastic with high mechanical strength is prepared by a new thermal processing method from a soft, melt-processable rubber. Compositions made by incorporation of equal-mass lignin, a renewable oligomeric feedstock, in an acrylonitrile-butadiene rubber often yield weak rubbers with large lignin domains (1–2 µm). The addition of zinc chloride (ZnCl2) in such a composition based on sinapyl alcohol-rich lignin during a solvent-free synthesis induces a strong interfacial crosslinking between lignin and rubber phases. This compositional modification results in finely interspersed lignin domains (<100 nm) that essentially reinforce the rubbery matrix with a 10–22 °C rise in the glassy-to-rubbery transition temperature. The ion-modified polymer blends also show improved materials properties, like a 100% increase in ultimate tensile strength and an order of magnitude rise in Young's modulus. Coarse-grained molecular dynamics (MD) simulations verify the morphology and dynamics of the ionomeric material. The computed result also confirms that the ionomers have glassy characteristics.

36 MATERIALS SCIENCE↗

DOE OSTI2018

A path for lignin valorization via additive manufacturing of high-performance sustainable composites with enhanced 3D printability

Here, we report the manufacture of printable, sustainable polymer systems to address global challenges associated with high-volume utilization of lignin, an industrial waste from biomass feedstock. By analyzing a common three-dimensional printing process—fused-deposition modeling—and correlating the printing-process features to properties of materials such as acrylonitrile-butadiene-styrene (ABS) and nylon, we devised a first-of-its-kind, high-performance class of printable renewable composites containing 40 to 60 weight % (wt %) lignin. An ABS analog made by integrating lignin into nitrile-butadiene rubber needs the presence of a styrenic polymer to avoid filament buckling during printing. However, lignin-modified nylon composites containing 40 to 60 wt % sinapyl alcohol–rich, melt-stable lignin exhibit enhanced stiffness and tensile strength at room temperature, while—unexpectedly—demonstrating a reduced viscosity in the melt. Further, incorporation of 4 to 16 wt % discontinuous carbon fibers enhances mechanical stiffness and printing speed, as the thermal conductivity of the carbon fibers facilitates heat transfer and thinning of the melt. We found that the presence of lignin and carbon fibers retards nylon crystallization, leading to low-melting imperfect crystals that allow good printability at lower temperatures without lignin degradation.

36 MATERIALS SCIENCE↗

DOE OSTI2017

An Acrylonitrile–Butadiene–Lignin Renewable Skin with Programmable and Switchable Electrical Conductivity for Stress/Strain-Sensing Applications

We report an approach for programming electrical conductivity of a bio-based leathery skin devised with a layer of 60 nm metallic nanoparticles. Lignin-based renewable shape-memory materials were made, for the first time, to program and restore the materials’ electrical conductivity after repeated deformation up to 100% strain amplitude, at a temperature 60–115 °C above the glass transition temperature (T g ) of the rubbery matrix. We cross-linked lignin macromolecules with an acrylonitrile–butadiene rubbery melt in high quantities ranging from 40 to 60 wt % and processed the resulting thermoplastics into thin films. Chemical and physical networks within the polymeric materials significantly enhanced key characteristics such as mechanical stiffness, strain fixity, and temperature-stimulated recovery of shape. The branched structures of the guaiacylpropane-dominant softwood lignin significantly improve the rubber’s T g and produced a film with stored and recoverable elastic work density that was an order of magnitude greater than those of the neat rubber and of samples made with syringylpropane-rich hardwood lignin. The devices could exhibit switching of conductivity before and after shape recovery.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Thermo-Responsive Polymers-Based on Source-Selective Lignins

In this study, thermomechanical properties of hardwood and softwood lignin-nitrile butadiene rubber composites were controlled by a thermal annealing process. The presence of thermally unstable linkages within the selected lignins provides free radical sources for crosslinking reactions. The measured dynamic mechanical properties demonstrated substantial improvement in glass transition temperatures (Tg) and storage moduli (E’) of 50 wt. % softwood lignin- and 50 wt. % hardwood lignin-rubber composites after thermal annealing at 180°C. An increase in Tg of approximately 18°C and more than 230% increasing E’ was achieved after annealing the 50 wt. % hardwood lignin-rubber for 5 h. The chemical crosslinking reactions between lignin-nitrile butadiene rubber and lignin-lignin were characterized by in-situ dynamic mechanical analysis and Fourier transform infrared (FTIR) spectroscopy. A mechanism of crosslinking reactions was revealed.

Nguyen, Ngoc A.↗