Bioplásticos de hidroxipropil metilcelulose obtidos por um método inovador: casting centrífugo

Abstract

Bioplastic-forming methods have been studied both to improve the physical- mechanical properties of the materials and to scale up their production. In line, the objective of this study was to develop and characterize hydroxypropyl methylcellulose (HPMC) bioplastic films produced by an innovative method: centrifugal casting. For this, the processing parameters were screened to determine the optimum range capable of ensuring complete film drying. The films were characterized as far as uniformity, anisotropy, behavior under flow, and morphology by means of analytical techniques such as tensile tests, X-ray diffractometry (XRD), infrared spectroscopy (FTIR), rheological tests, and electron microscopy (SEM). The screening showed that HPMC at 2% (w/w) led to film drying within 60 min, whereas 5% (w/w) caused Weissenberg effect. The temperature of 110 oC and rotation speed of 2800 r.p.m. caused heterogeneous drying with appearance of whitish regions on film surface. At drying temperature of 40 oC and time of 3 h and 45 min, homogeneous films were obtained. None of the films presented uniformity of thickness. The mechanical tests did not suggest anisotropic behavior. FTIR spectra indicated no spectral differences among the casting techniques. The crystallinity of the pure HPMC powder and the films produced by bench and centrifugal casting were 48%, 36% and 28%, respectively. According to the flow curves and viscosity profiles, all samples showed pseudoplastic behavior, and the viscosity decreased with increasing temperature. The HPMC films showed surface instability like the phenomenon known as "shark skin" or "orange peel". SEM images revealed that the surface of the 3.5% HPMC film prepared by bench casting was smooth and continuous, but the sample prepared by centrifugal casting showed grooves. Finally, the film formed at 110 °C and 2800 r.p.m. resulted in a surface with fractures and wear.