Biodegradation of PLA/CNC composite modified with non-ionic surfactants

Poly(lactic acid) (PLA) undergoes degradation through the action of microorganisms and enzymes that can degrade it by composting. The goal of this work was to observe the degradation/disintegration behavior in garden soil of neat PLA and PLA composites with 3 wt% cellulose nanocrystals (CNC) modified or not with non-ionic surfactants (S) at a weight ratio of 1:1 (CNC:S). Four types of non-ionic surfactants with hydrophilic-lipophilic balance (HLB) ranging from 4.3 to 16.7 were tested: sorbitan monolaurate (Span 20), sorbitan monooleate (Span 80), polyoxyethylene sorbitan monolaurate (Tween 20) and polyoxyethylene sorbitan monooleate (Tween 80). Films were obtained by solution casting, cut into 2 x 2 cm strips and buried in garden soil, while monitoring the temperature and humidity for 150 days. Changes in the films by visual inspection, polarized light microscopy, thermogravimetric analysis (TGA) and Fourier-transform infrared spectroscopy (FTIR) were observed. Results showed that the addition of surfactants favored the rate of biodegradation of the composites, being the lowest molecular weight the determinant property of the surfactant to enhance biodegradation rate of PLA/CNC/S composites. Nevertheless, for surfactants belonging to the same chemical family, the highest biodegradation rate for PLA/CNC/S composite obeys the principle of high HLB, and low spherulite size.

Automated summary

This study aimed to observe the degradation behavior of neat PLA and PLA composites with cellulose nanocrystals (CNC) in garden soil, and investigate the effect of adding surfactants on the degradation rate. The results showed that the addition of surfactants can enhance the biodegradation rate of the composites, with the molecular weight of the surfactant playing a decisive role. Among surfactants belonging to the same chemical family, the PLA/CNC composite with higher HLB and smaller spherulite size exhibited the highest biodegradation rate.