Enhanced permeability of cellulose acetate ultrafiltration membrane by incorporation of cellulose graft copolymer

In this research, a series of cellulose acetate (CA)-based blend ultrafiltration (UF) membranes bearing poly(ε-decalactone) (PDL)-grafted cellulose copolymer (i.e., CgD) of 1 wt% (M1), 3 wt% (M2), 5 wt% (M3), and 10 wt% (M4) was fabricated and comprehensively characterized to enhance the permeation performances of the neat CA membrane (M0). The structural/thermal properties, morphological changes, pore characteristics, and separation performances were identified to investigate the effect of CgD incorporation on the CA/CgD blend UF membrane series (i.e., from M1 to M4). It was revealed that the CA and incorporated CgD copolymer showed partial compatibility due to the weak physical interactions rather than chemical interactions. We found that the introduction of CgD into the CA-based blend system was favorable to generate enlarged finger-like macropores in the sub-layer and a thinner top surface layer compared to the neat CA membrane. This result can be attributed to the fact that blending of CgD lowered the high affinity of CA towards non-solvent, eventually led to an instantaneous demixing behavior. Furthermore, all the CA/CgD blend UF membranes displayed a slightly smaller mean pore size with a narrow pore size distribution in the surface layer than those for the neat CA membrane (M0). These are thought to be due to the formation of more slender channels in the top surface layer induced by the incorporation of the CgD, which exhibited weak physical interaction with CA matrix. The prepared M2 membrane (CA/CgD membrane having 3 wt% of CgD) had a greatly higher pure water flux (PWF) and rejection (%) properties (~ 13.5 L/m2h and 90.0%, respectively) as compared to the case for M0 (~ 1.2 L/m2h and 84%, respectively). Meanwhile, all the prepared CA/CgD membranes (M1–M4) exhibited the analogous antifouling properties without a drastic decrease as compared to the neat CA membrane (M0). Our research may open the possibility for designing of fully bio-resource-based and sustainable membranes with enhanced membrane permeation performances.