Ruijuan Zhou

• The present work focuses on the structure-property relationships of particulate-filled thermoplastics and thermoplastic elastomer (TPE). In this work two thermoplastics and one TPE were used as polymer matrices, i.e. amorphous bisphenol-A polycarbonate (PC), semi-crystalline isotactic polypropylene (iPP), and a block copolymer poly(butylene terephthalate)-block-poly(tetramethylene glycol) TPE(PBT-PTMG). For PC, a selected type of various Aerosil® nano-SiO2 types was used as filler to improve the thermal and mechanical properties by maintaining the transparency of PC matrix. Different types of SiO2 and TiO2 nanoparticles with different surface polarity were used for iPP. The goal was to examine the influence of surface polarity and chemical nature of nanoparticles on the thermal, mechanical and morphological properties of iPP composites. For TPE(PBT-PTMG), three TiO2 particles were used, i.e. one grade with hydroxyl groups on the particle surface and the other two grades are surface-modified with metal and metal oxides, respectively. The influence of primary size and dispersion quality of TiO2 particles on the properties of TPE(PBT-PTMG)/TiO2 composites were determined and discussed. All polymer composites were produced by direct melt blending in a twin-screw extruder via masterbatch technique. The dispersion of particles was examined by using scanning electron microscopy (SEM) and micro-computerized tomography (μCT). The thermal and crystalline properties of polymer composites were characterized by using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The mechanical and thermomechanical properties were determined by using mechanical tensile testing, compact tension and Charpy impact as well as dynamic-mechanical thermal analysis (DMTA). The SEM results show that the unpolar-surface modified nanoparticles are better dispersed in polymer matrices as iPP than polar-surface nanoparticles, especially in case of using Aeroxide® TiO2 nanoparticles. The Aeroxide® TiO2 nanoparticles with a polar surface due to Ti-OH groups result in a very high degree of agglomeration in both iPP and TPE matrices because of strong van der Waals interactions among particles (hydrogen bonding). Compared to unmodified Aeroxide® TiO2 nanoparticles, the other grades of surface modified TiO2 particles are very homogenously dispersed in used iPP and TPE(PBT-PTMG). The incorporation of SiO2 nanoparticles into bisphenol-A PC significantly increases the mechanical properties of PC/SiO2 nanocomposites, particularly the resistance against environmental stress crazing (ESC). However, the transparency of PC/SiO2 nanocomposites decreases with increasing nanoparticle content and size due to a mismatch of infractive indices of PC and SiO2 particles. The different surface polarity of nanoparticles in iPP shows evident influence on properties of iPP composites. Among iPP/SiO2 nanocomposites, the nanocomposite containing SiO2 nanoparticles with a higher degree of hydrophobicity shows improved fracture and impact toughness compared to the other iPP/SiO2 composites. The TPE(PBT-PTMG)/TiO2 composites show much better thermal and mechanical properties than neat TPE(PBT-PTMG) due to strong chemical interactions between polymer matrix and TiO2 particles. In addition, better dispersion quality of TiO2 particles in used TPE(PBT-PTMG) leads to dramatically improved mechanical properties of TPE(PBT-PTMG)/TiO2 composites.