Enzymatic degradation of cellulosic fabrics modified with atomic layer deposited aluminum oxide thin films

Cellulose is a sustainably sourced material with broad applications ranging from structural reinforcements to biomedical devices. Atomic layer deposition (ALD) has been used to enhance the properties of cellulosic materials, but retaining biodegradability is important for various applications that require circularity to materials usage. Here, we explore how ALD of nanoscale AlOx films onto cellulosic fabrics impacts enzymatic degradation. Energy dispersive x-ray analysis and x-ray photoelectron spectroscopy (XPS) are used to confirm alumina deposition onto cellulosic fabrics. At even 1 ALD cycle, roughly 0.1 nm of alumina, enzymatic degradation is initially significantly reduced relative to an uncoated fabric. However, beyond about 10 cycles, only marginal additional reductions in degradation rate are observed, and this reduced degradation is only apparent after a few days. XPS reveals that ALD coatings of <10 cycles etch away upon immersion in the enzymatic solution within 3 days, effectively turning the treated fabric into a neat fabric. In contrast, cellulose coated with >10 cycles retain their alumina coatings for the entire 5-day test period, partially explaining the “plateau” in the degradation rate. Beyond 10 ALD cycles, SEM images reveal conformal coatings that begin to crack after two or more days of immersion in water. These cracks are postulated to be the primary pathways for enzymatic attack of the underlying fabric, leading to similar degradation rates in these thicker ALD coatings. In summary, we find that ALD coated cellulosic fibers have a delayed biodegradation response that is explained by either coating dissolution or cracking depending upon the coating’s thickness.