High-impact resistance polymeric composite: characterization and simulation
Creators: name: Zhao, Jiawei
Publisher: name: Loughborough University
Year: 2019
Subjects: subject: 91299 Materials Engineering not elsewhere classified
subject: FOS: Materials engineering

description: The PhD thesis investigates toughening of polymer nanocomposites in terms of processing, characterization and simulation. Two different nanocomposite systems were addressed, which are polypropylene/nano calcium carbonate (PP/nCC) and polycarbonate/Polyhedral Oligomeric Silsesquioxane(PC/POSS). The first part of the thesis focuses on processing and characterization of the PP/nCC. Batch-process and continuous liquid assisted extrusion were performed. PP nanocomposite containing 0~3wt.% nCC were prepared by those method and further moulded by compression moulding. Impact resistance of the samples were obtained by falling weight impact tester. The dispersion of nCC in the samples prepared from different methodology was compared using SEM. As liquid was involved during processing, DSC and TGA were used to determine the amount of residual liquid phase in the product. The impact resistance of PP/nCC is peaked at the continuous liquid assisted processed sample which contain 2.0 wt.% nCC powder. For this loading of nCC, A roughly 300% increment compare to the pure PP is obtained on energy absorption during FWIT test. Among all process technique based on extrusion, SEM results indicate a better quality of dispersion is achieved by continuous liquid-assisted process compared with directly dry mixing and batch-processed. DSC and TGA results indicate the final products are free from residual liquid phase. DSC results also indicate that the nCC powder promote the crystallization of PP. TGA results indicate that the thermostability of PP is enhanced by introduce well dispersed nCC powder. Toughening mechanism is concluded by analysis of the fracture SEM image. The second part focus on the characterization and numerical simulation of PC/POSS nanocomposite. The aim is to investigate how POSS molecule interact with PC and affect its performance in terms of the tensile properties and toughness. Three grade of PC containing 0 to 0.3 wt. % of POSS is melt blended. The impact resistance of the PC/POSS samples are obtained by FWIT. The tensile properties of the samples are obtained by tensile tester. Fracture surfaces are observed by SEM. Depends on grade, a 30%~150% increment in energy absorption is obtained for PC/POSS nanocomposite. Molecular dynamics simulations are used to answer two questions. The first one is how the POSS particle interact with PC chains. As the PC used contains Si-OH group, possibility of the hydrogen bond formation is investigated. However, the result indicates the hydrogen bond is hardly formed between POSS and PC chains. The reason maybe the stereo effect. On the other hand, after comparing with different structure of POSS, the organic shell part of POSS turns to be the dominate factor of the PC-POSS interaction. The second question is how the POSS affected mechanical performance of PC. Tensile, compression, shear and impact simulation are conducted for PC and PC/POSS system. During tensile simulations, the present of the POSS increase the elongation at yield, which agree with the experiment. During compression simulations, POSS molecules turn to have a stereo effect by its high stiffness. During shearing simulations, POSS molecules absorb energy and deform. During impact simulations, PC/POSS system absorb more energy by interfacial debonding. As suggested by previous research that POSS improved the sustainability of the polymer matrix, Simulations have been conducted to mimic the oxidization at low earth orbit. The result indicates POSS increase the stability of the PC in such condition.