Bacterial cellulose nanocrystals: from obtaining, under different hydrolysis conditions, the incorporation as reinforcement in poly(L-lactic acid)

ABSTRACT This work aimed to produce bacterial cellulose, to obtain bacterial cellulose nanocrystals, to incorporate nanocrystals as a reinforcement in poly(L-lactic acid) and to evaluate the properties of these bionanocomposites. Bacterial cellulose membranes from the bacterium Gluconacetobacter hansenii were produced. From the membranes were obtained nanocrystals by hydrolysis with sulfuric acid (H2SO4), based on 11 experiments. The parameters varied in the experiments were: concentration of H2SO4, temperature and time. It is possible to define criteria for obtaining nanocrystals by thermogravimetric analysis and analysis of dynamic scattering of light. Main results indicate the possibility of obtaining in the condition of: 80% concentration of H2SO4 (m/m), 60 °C and 60 min. For this condition, suitable sizes of the nanocrystals (mean 388 nm), suitable zeta potential (-38 mV) and adequate thermal stability (Tonset2 = 301.9 °C) were obtained. Subsequently, nanocrystals obtained according to defined criteria were incorporated into poly(L-lactic acid) in two concentrations (2,5 and 5%), using two methods (without and with functionalization of nanocrystals). The prepared bionanocomposites were characterized by thermogravimetric analysis and differential explanatory calorimetry. Results of the techniques of characterization of bionanocomposites were compared with results of pure poly(L-lactic acid). Main results regarding the methods, reveal the importance of the functionalization of the nanocrystals before incorporating them to the poly(L-lactic acid). On the reinforcement concentration used, the increase of the thermal stability was gradual, according to reinforcement content, and for the bionanocomposite with 5% functionalized nanocrystals the increase was of 10,4 ºC in the Tonset2 in relation to the poly(L-lactic acid) pure. However, the degree of crystallinity decreased (Xc of pure PLLA = 40,38% and Xc of bionanocomposite with 5% of functionalized nanocrystals = 24,73%). It is concluded that the addition of bacterial cellulose nanocrystals in poly(L-lactic acid) is environmentally feasible and improves properties.