Cellulosic Nanocomposites for Advanced Manufacturing: An Exploration of Advanced Materials in Electrospinning and Additive Manufacturing

Abstract

The effects of formulation and processing of thermoplastics and composites containing Nanocrystalline Cellulose (NCC) were explored and characterized for electrospinning and fused deposition modeling 3D printing advanced manufacturing techniques.

Through electrospinning, desirable outcome responses were optimized through design of experiments for electrospun fibers of 3 material systems by controlling up to four formulation and processing factors. Regression models were developed for fiber diameter, beading density, and bead diameter responses for each material system and improved with center point measurements where applicable. The three material systems include: NCC and polycarbonate (PC) in a mixture of tetrahydrofuran and dimethylformamide (THF:DMF), NCC and PC in chloroform, and NCC and polyamide-6,6 (PA 6,6) in formic acid.

For NCC and PC in THF:DMF, the inclusion of NCC tended to improve the spinnability of the system. Less beading, smaller fibers, and more pristine fibers were observed with the incorporation of 2-wt.% of NCC with PC. NCC surface modified with (2-dodecen-1-yl) succinic anhydride (cNCC) and PC in chloroform was the least ideal system tested, as it had a very narrow window of parameters to achieve desirable fibers. Concentrations of PC are required to be greater than 15-wt.% to achieve some fibers and this was improved through the addition of cNCC, but the resulting uniformity and repeatability of the chloroform solvent was not ideal for the current benchtop experimental setup. Modified cNCC and PA 6, 6 lead to the most desirable fibers, with 200 to 300 nm fiber diameters that can lead to desired nanoscale effects, like extremely high surface area and slip-flow filtration benefits. The cNCC and PA 6,6 system did not include any beading and produced a regression model for fiber diameter that has an R-squared fit of 0.999, making it excellent for producing desired fiber diameters.

Proof of concept application of electrospun fibers in transparent coatings with improved surface properties were presented and validated through microhardness and light transmittance testing.

Through fused deposition modeling thermoplastic starch-resin copolymer (TPS) and NCC reinforced TPS was explored. 3D printer filaments were designed and manufactured on a benchtop scale extruder as well as in a scale-up facility used for industrial production. ASTM specimens were 3D printed on the Makerbot Replicator 2X printer with Gcode and slicing parameters optimized for the new formulation. Mechanical properties were measured for impact, tensile, and flexural testing.

3D Printing slightly increased tensile and flexural modulus relative to injection molding techniques, while only slightly decreasing impact, flexural and tensile strength, suggesting that 3D printing may be a suitable replacement process for certain applications. The addition of NCC to TPS increased tensile and flexural modulus at 1, 3, and 5-wt.% loadings while the addition of NCC increased impact, tensile and flexural strength to a maximum at 3-wt.% loading. Scale-Up trials were successful at preparing NCC/TPS filaments for 3D printing, but in general, mechanical properties were at about 65-80% of the desktop filament extrusion.