Durability of Ultem 9085 in Marine Environments: A Consideration in Fused Filament Fabrication of Structural Components.

The long-term durability of polymer components produced by additive manufacturing (AM) in marine conditions is poorly understood. Here, fused filament fabrication (FFF) of Ultem 9085 was conducted and accelerated aging was performed. Two printing orientations (-45/45° and 0/90°) and two sample types (ASTM D638 Type 1 and Type 4) were produced and subjected to accelerated aging in either seawater or air. Results from tensile tests showed that the elastic modulus, yield strength and ultimate tensile strength increased after seawater aging, whereas the elongation to failure decreased. Results of thermogravimetric analysis (TGA) and derivative-TGA curves indicated that hydrolysis occurred after seawater exposure to the polycarbonate (PC) component and changes in structure or hydrogen bonds formed in the polyetherimide (PEI) component. Differential scanning calorimetry showed that physical aging occurred after short exposure periods and low temperature. Longer exposures and higher temperatures resulted in increasing plasticization by water and scission of the PC molecules. Results from Raman suggest that hydrolysis of the PC occurred, with a reduction in free volume produced by physical aging or hydrogen bonding with water molecules. These results highlight that Ultem 9085 is susceptible to degradation in marine environments, and there are two primary mechanisms, including physical and chemical aging. Their specific contribution is highly sensitive to the aging temperature and require careful selection in accelerated aging evaluations.

Polyelectrolyte Complex Coacervate Assembly with Cellulose Nanofibers.

Polyelectrolytes are used in paper manufacturing to increase flocculation and water drainage and improve mechanical properties. In this study, we examine the interaction between charged cellulosic nanomaterials and polyelectrolyte complex coacervates of weak polyelectrolytes, polyacrylic acid salt, and polyallylamine hydrochloride. We observe that by changing the order of addition of the polyelectrolytes to cellulose nanofibers (CNFs), we can tune the interactions between the materials, which in turn changes the degree of association of the coacervates to the CNFs and the rate at which they aggregate. Importantly for the papermaking process, when adding the polyelectrolytes sequentially to the CNFs, we found faster aggregation to the fibers and lower water retention values compared to those when preformed coacervates or CNFs by themselves were used. Coarse-grain molecular dynamic simulations further support the fundamental mechanism of aggregation by taking into consideration the interaction between cellulose and the complexes at the molecular level. The simulations corroborate the experimental observations by showing the importance of strong electrostatic interactions in aggregate formation.