Rheological investigation on polyethylene terephthalate (PET) filled with hollow glass beads

A composite of polyethylene terephthalate (PET) and hollow glass beads (HGB) with two different HGB sizes was prepared and investigated rheologically. When the HGB content reaches approximately 30 wt%, the PET/HGB composite changes from a Newtonian fluid to a pseudoplastic one within the measured frequency range. If the HGB content is below the critical value, the viscosity of the composite may be lower than that of the neat PET melt. This is because scrolling or sliding of the HGB in the PET melt increases the apparent shear rate and reduces the torque measured by the rheometer rotor. Meanwhile, the size of the HGB affects the viscosity of the composite. The 40 mu m HGB has a more pronounced effect, resulting in higher viscosity than 50 mu m HGB. Furthermore, the composite containing 40 mu m HGB has a lower density than the one containing 50 mu m HGB. This is because the 40 mu m HGB has a lower breaking rate and higher volume fraction compared to the 50 mu m HGB at the same mass fraction. The peak relaxation time of the PET/HGB composite increases with the HGB content, and higher temperatures correspond to shorter relaxation times. DSC analysis showed that the addition of HGB filler decreased the melting temperature and increased the crystallization temperature of the PET material. Since the PET/HGB composite has a longer relaxation time than pure PET, the corresponding aggregates made of PET chains and HGBs are expected to have larger characteristic sizes compared to PET and HGB. These sizes can be determined approximately using a grid drawing method. The coupling agent CS-101 enhances the bonding between PET and HGB. This is evidenced by comparing the viscosity curves of the composite with and without the coupling agent. Highlights The polyethylene terephthalate (PET)/hollow glass beads (HGB) composites with low levels of HGB might exhibit unusual viscosity. Abnormal viscosity in molten PET occurs due to the rolling or sliding of HGB. The composites with high HGB levels may exhibit a solid-like modulus plateau. The proposed aggregate consists of PET, HGB, and broken glass shards.