Effect of Polydopamine Coating of Cellulose Nanocrystals on Performance of PCL/PLA Bio-Nanocomposites

Abstract

In bio-nanocomposites with a poly(lactic acid) (PLA)/poly(ε-caprolactone) (PCL) matrix with neat and polydopamine (PDA)-coated cellulose nanocrystals (CNCd), the use of different mixing protocols with masterbatches prepared by solution casting led to marked variation of localization, as well as reinforcing and structure-directing effects, of cellulose nanocrystals (CNC). The most balanced mechanical properties were found with an 80/20 PLA/PCL ratio, and complex PCL/CNC structures were formed. In the nanocomposites with a bicontinuous structure (60/40 and 40/60 PLA/PCL ratios), pre-blending the CNC and CNCd/PLA caused a marked increase in the continuity of mechanically stronger PLA and an improvement in related parameters of the system. On the other hand, improved continuity of the PCL phase when using a PCL masterbatch may lead to the reduction in or elimination of reinforcing effects. The PDA coating of CNC significantly changed its behavior. In particular, a higher affinity to PCL and ordering of PLA led to dissimilar structures and interface transformations, while also having antagonistic effects on mechanical properties. The negligible differences in bulk crystallinity indicate that alteration of mechanical properties may have originated from differences in crystallinity at the interface, also influenced by presence of CNC in this area. The complex effect of CNC on bio-nanocomposites, including the potential of PDA coating to increase thermal stability, is worthy of further study.

The Effects of the Deacetylation of Chitin Nanowhiskers on the Performance of PCL/PLA Bio-Nanocomposites

“…Due to the poor “visibility” of CNW in polymer systems [ 35 ], estimation of its localization is based on the dominancy of kinetic factors [ 45 ], like targeted pre-blending, over thermodynamic ones [ 46 ]. The reason is the limited migration of the relatively large nanoparticles during short-time melt mixing.…”

“…Taking into account certain negative effects of DMF on the polyesters applied [ 35 ], CNW-free blends were also prepared using DMF-treated (analogously to masterbatch preparation) components. The different structures for PLA DMF /PCL and PCL DMF /PLA ( Figure 3 ), especially lower continuity and higher amounts of the PLA subinclusions inside the PCL phase for PLA DMF confirm the altering of rheological parameters and, thus, also of dynamic asymmetry [ 26 ] by DMF.…”

“…These structural changes are more pronounced with increasing CNW content. Due to a more marked decrease in the viscosity of PLA by both CNW 1 and CNW 2 ( Figure 2 ) and the mentioned dominant presence of CNW in this phase, the application of PLA pre-blends leads to lower continuity of this phase (in contrast to nonreactive CNC [ 35 ]). Further, important effects on structure originate from CNW bonded to polymers ( Scheme S1 ) and CNW localized at the interface.…”

“…Similar results were observed in systems with MMT, HNT and CNC. For instance, 2% CNC led to slight decrease for PLA and increase for PCL [ 35 ].…”

“…A few studies using organic NF in PCL/PLA deal mostly with cellulose nanocrystals (CNC) [ 19 ], including PCL- and PLA-grafted CNC [ 6 , 7 ]. Recently, we have revealed the role of CNC and dopamine-coated CNC in PCL/PLA of different blend ratios [ 35 ]. In the case of CNW application in biodegradable polyesters, aminolysis must also be considered [ 20 , 36 ].…”