Performing Department
(N/A)
Non Technical Summary
The long-term goal of the project team is to develop new and sustainable bioproducts from non-food biomass. We envision these products will be environmentally and economically sustainable, and they will enable Americans to enjoy their current lifestyle in a sustainable manner. The objective of this proposal is to create a sustainable material comprised of agriculturally derived components that will enable large-format 3D printing. We hypothesize that suitable chemical reactions between plant-derived materials will provide new strong and tough plastics that can be derived from soybean oil and plant materials. We will use a variety of high-tech materials characterization techniques to test our hypothesis. If realized, these new materials represent breakthroughs that will have a significant positive impacts on industries working in additive manufacturing and biorefining. Moreover, scientists working in the fields of materials science and biomass chemistry will benefit greatly from the knowledge gained from these experiments. Finally, residents of rural communities that provide biomass feedstocks for these efforts will ultimately benefit as these developments are scaled up and deployed.
Animal Health Component
50%
Research Effort Categories
Basic
35%
Applied
50%
Developmental
15%
Goals / Objectives
The goal of this project is to create and characterize a sustainable resin material comprised of agriculturally derived components that will enable large-format 3D printing by stereolithography. The first objective is to identify methods to enhance interactions between cellulose nanomaterials in lignin photopolymer matrices. The second objective is to identify approaches to enhance mechanical toughness and thermal stability of new 3D printing resins.
Project Methods
We will begin our studies by isolating lignin using the CELF process. Accordingly, we will isolate lignin from mixed hardwoods, southern yellow pine, and switchgrass. This will afford us a hardwood, a softwood, and an agricultural lignin material to test, and will allow us to comment on any natural variation present among the materials created from different biomass species.The biomass is heated in a mixture of water, THF, and sulfuric acid catalyst to 160-180 °C for 15-30 minutes. The process conditions afford variations in lignin quality and structure, and we will investigate the effect of these on the structure-property relationships in lignin-containing resins we create. The lignin fraction is isolated by solvent-solvent extraction, concentrated, and finally dried under reduced pressure at 40 °C to afford highly pure lignin powder.We will characterize the lignin using a variety of techniques, including NMR spectroscopy, size-exclusion chromatography (SEC), differential scanning calorimetry (DSC), and UV-Vis spectroscopy. Together, these experiments represent an accounting of the structural, thermal and photo properties of each lignin sample.For lignin to be used in a photopolymer resin, we must modify it by esterification to install photoactive acrylate groups. We have chosen two sets of modifications based upon whether we want to create a hydrophobic or hydrophilic lignin resin. In principle, the two modifications methods are identical except for the identity of the group we will append.For our first approach, we have chosen methacrylic anhydride as the modifying agent to install methyl methacrylate esters onto lignin (ML). For lignin samples that have limited solubility in neat methacrylic anhydride, the lignin can also be dissolved in 1,4-dioxane before adding methacrylic anhydride. The mixture is heated to 60 °C for 48 h and then cooled to room temperature and quenched with sodium bicarbonate solution, which causes the modified lignin to precipitate. This material is isolated by vacuum filtration and washed with water until the washings have a neutral pH. The isolated material is then dried at 40°C at reduced pressure for 16 h.For our second approach, we wish to create a hydrophilic lignin resin and then incorporate unmodified hydrophilic TOCNFs. We hypothesize that the hydrophilic character of the resin will allow for the unmodified TOCNFs to disperse more readily than in a hydrophobic resin. For this approach, we have chosen itaconic anhydride as the modifying agent to install itaconic acid esters onto lignin (IL). This chemistry is accomplished in an identical way to that described above for methacrylic anhydride, and the resulting lignin material is characterized in the same manner.For TOCNFs to be incorporated into the hydrophobic resin described, we will need to modify its surface with a surfactant to increase its dispersibility. To do this, we will use TOCNFs that we purchase from the University of Maine Forest Products Laboratory. These will be suspended in 300 mL deionized water at 1 weight percent and homogenized. Then, we will add lauric arginate ethyl ester (LAE) dropwise at a 1:6 TOCNF:LAE ratio to afford LAE-coated TOCNFs.With lignin resins and TOCNFs in hand, we will set about to formulate the lignin-TOCNF resins. For the fiber approach, we will use a mixture of ML and LAE-coated TOCNFs, and for the matrix approach, we will use a mixture of IL and unmodified TOCNFs. Both dispersions will be carried out in an identical manner and will be described once below.Lignin samples will be diluted using a reactive diluent. We will employ either 1,6-hexanediol diacrylate (HDODA) or acrylated epoxidized soybean oil (AESO) for this purpose. We will explore both diluents to determine a baseline set of performance properties that depend on the ratios of lignin and TOCNFs present in the diluent. Mixtures will consist of 5-25% by weight TOCNF in lignin, and they will be diluted with 0-50% diluent. We will employ Diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) as our photoinitiator using a 1 weight percent concentration.Once produced, we will cast films of the lignin-TOCNF resins by pouring them onto 3 cm squares of borosilicate glass pretreated with a small spray of Teflon mold release. Once cured, the 1-mm thick films will be removed from the glass slides (facilitated by using the Teflon mold release), and the films will be cut with an ASTM-D638 Type V tensile testing specimen die. With this setup, we can produce 3-4 specimens per cast film having the proper dimensions as described in the ASTM D-638 standard for tensile testing of plastics.Tensile bars will be loaded into an Instron universal testing machine to conduct static tensile tests. These tests will be performed in at least triplicate per TOCNF-lignin loading in each diluent to ascertain ultimate tensile strength, percent elongation, and toughness of the samples. These will be compared to baseline values for lignin in each diluent to measure the effect of TOCNF concentration on those properties. In addition, we will use scanning electron microscopy at the broken edges to visually inspect for fiber dispersion and morphology. We will also employ a Bruker Hysitron TI-980 Triboindenter to investigate the evolution of performance properties between the lignin matrix and the TOCNF fibers using nanoindentation, since we are ultimately interested in how these composite materials perform at the matrix-fiber nanointerface. We will conduct nanoindentation tests of a control specimen that contains only lignin in each diluent and compare those to the TOCNF-lignin composites. We will also employ the Accelerated Property Mapping technique, which will allow us to visualize the TOCNFs in the matrix by monitoring changes in displacement and modulus of the nanoindenter.We will blend 3D printer resins by diluting the pre-cured materials with AESO and TPO. In this way, all the components will be blendable and cured simultaneously in the printer. We will also be able to adjust concentrations of lignin, TOCNF, AESO, TPO, and any reactive diluent required (e.g. HDODA). This will allow us to study the effect of concentration of each of these materials on the performance properties of the liquid material and objects printed using it. Materials will be added to an opaque polypropylene jar and mixed using a Thinky ARE-310 kinetic mixer capable of producing 510 G of acceleration in rotation and revolution to fully mix these materials.We will measure a pair of performance properties of the liquid materials relevant to its ability to act as a 3D printer resin, including resin viscosity with a TA Instruments AR-G2 rheometer with a cone-and-plate geometry over a range of shear rates from 0.1 to 100 Hz at 25 °C, and their working curves, using an as-produced 3D model with dimensions of 40 × 60 mm2 consisting of 32 squares of varying thickness ranging from 5 to 20 layers.Finally, we will use SOLIDWORKS to create ASTM D638 Type V tensile testing specimens. Our Elegoo Mars 2 Desktop 3D printer has a build platform that will accommodate 10 such specimens simultaneously. We will print each specimen twice, at 90° orientations from each other, to ensure the performance properties we test below are not anisotropic. Once we verify this, we will print testing specimens in the parallel orientation to maximize printing speed. Tensile testing specimens will be washed with 2-propanol, dried with a stream of compressed air, and post-cured using the Hg arc lamp described above for 10 s on each side. These materials will then be ready for tensile testing using the Instron universal testing machine. We will construct stress-strain curves to compare ultimate tensile strength, percent elongation, and toughness of each sample.