Effects of magnesium borate on the mechanical performance,thermal and chemical degradation of polyethylene terephthalate packaging material

Abstract

This study is on polyethylene terephthalate (PET) compounded with magnesium borate (MB) (Mg₂B₂O₅) powders between (0.2–3.2% by weight) which were synthesized via sol-gel technique at laboratory-scale. The MB/PET composites were characterized in terms of chemical, thermal degradation, and mechanical properties. Their phases and chemical structures were identified by X-ray Diffraction and Fourier Transform Infrared analyses. The MB added into PET matrix significantly reduced PET degrading to acetaldehyde, carboxylic acids and diethylene glycol. However, while at 0.2 wt.% MB isophthalic acid (IPA) decreased and at higher MB concentrations there were higher IPA levels. The added MB increased the composites intrinsic viscosity (IV) compared to the pure PET. The highest IV (0.701 dL/g) was at the 0.2 wt.% MB/PET composite. Both T_g and T_m temperatures trended down up to 3.2 wt.% MB. Compared to pure PET, glass transition temperature (T_g) decreased to 80.4°C (at 3.2 wt.% MB) from 81°C, whereas melt temperature (T_m) decreased to 248.5°C (at 3.2 wt.% MB) from 249.4°C. The MB/PET composite tensile strength increased by 11.31% to a 60 MPa maximum at 0.2 wt.% MB compared to neat PET (53.9 MPa). However, at 0.4 wt. % and higher MB the dispersion was insufficient causing the MB powders to aggregate in the PET matrix, resulting in reduced tensile strength.