Investigation Of The Preparation And Properties Of Poly (lactic Acid) / Epoxy Polyhedral Oligomeric Silsesquioxanes Nanocomposites

Poly(lactic acid) (PLA) is one of the most widely used biobased-plastics which are themost mature of industrialization. However, the further appliacations of PLA have beenrestricted by its weaknesses. Epoxidized polyhedral oligomeric silsesquioxanes (EVOS)posses reactive epoxy groups and thermal stability, it might be used as functional filler toimprove the overall mechanical properties of PLA .The PLA/EVOS composites prepared in an internal mixer via melt blending, and themechanical properties, rheological properties and crystallization kinetics of the compositeswere characterized in terms of infrared spectrometer, scanning electron microscopy, dynamicmechanical thermal analyzer, tensile testing machine, capillary rheometer and DSC.The results of mechanical properties revealed that the impact strength at 5 wt% EVOSloading, the tensile strength at 1 wt% EVOS loading and the elongation at break at 0.5 wt%EVOS loading were increased by 22.8%, 8.3% and 68.9% compared to pure PLA,respectively. The DMA results showed that the storage modulus of PLA/EVOSnanocomposites increased initially and then decreased with the increase of the EVOS content,the maximal storage modulus was obtained in the case of 0.5 wt %, increased by 49% versuspure PLA. The SEM images reflected that the incoration of EVOS can initiate the formationof massive crazes, which absorbed more impact energy under external force and thusimproved the toughness of PLA.PLA/EVOS nanocomposites is pseudoplastic fluid, non Newtonian index increased withthe increasing temperature; and non Newtonian index tended to increase and then decreasewith the increase of the EVOS content.The values of avrami index for pure PLA and its nanocomposites were in the range or 2.15~2.62 and 2.24~2.66, respectively. It is inferring that the nucleation and growth mode ofpure PLA and its nanocomposite were similar, including two-dimensional disc growth andthree-dimensional spherulites growth. The analysis results of Jeziorny method showed that inthe case of the same heating rate, the crystallization rate constant Zc increased with increasingof EVOS content and was up to the maximum at 1 wt% EVOS. The results of Mo methoddemonstrated that the F(T) andαincreased with the increase of EVOS content in the case ofthe same relative crystallinity. The crystallization activation energy calculated viaHoffman-Laruitzen theory that indicating that the crystallization rate increased as thetemperature decreased. The POM images revealed that the spherulite size at crystallized at130℃was far larger than that crystallized at 120℃. With increasing the EVOS contents, thespherulite size becomes smaller while more spherulites formed.