Investigation on the quantitative analysis and upgrading of recycled plastic composites and blends

The use of recycled plastics is economical and environmentally friendly. However, without scientific classification and quality control systems, the potential value of recycled plastics will be limited. This thesis aims at providing an analysis of the classification technique, modification options, and process optimization for quality improvement and control of recycled polymer composites and blends. Laboratory evaluation of the infrared (IR) spectroscopy on the quantitative analysis of polymer composites made from polypropylene (PP) and talc was performed. Attenuated total reflectance (ATR) accessory was used for the quantification due to its advantages of rapid analysis and no sample preparation. Due to the short penetration depth (0.5-3 μm) of IR beam from the ATR, the influence of talc homogeneity in PP on the accuracy of quantitative analysis has been discussed. Through four-time multiple extrusions of PP/talc composites, a more accurate calibration was established with the coefficient of determination (R2) increased from 0.910 to 0.996 compared to the single-time extruded calibration. Based on the calibration results, the prediction was made on compositional analysis of PP/talc composites waste from the automobile industry. Mechanical properties of obtained recycled composites were evaluated and controlled according to the compositional information. Correlations were found between the composition and mechanical properties of recycled PP/talc, which indicates the potential of IR quantitative analysis on the quality control of polymer composites waste. Upgrading polymer blends of PP and PET (polyethylene terephthalate) through compatibilization was evaluated in terms of morphological and mechanical properties. Compatibilization effect of SEBS (triblock copolymer styrene/ethylene butylene/styrene) and its functionalized elastomer grafted with maleic anhydride (MA) SEBS-g-MA have been compared. Enhanced interaction between the PP and PET phase was observed from the SEBS-g-MA compatibilized PP/PET blends due to the reaction of the MA content with PET end functional group (carboxyl). The optimization of SEBS-g-MA amount on the compatibilization of 80PP/20PET blend was also investigated in this study. When the amount of SEBS-g-MA is 10 phr (part per hundred resin), the unnotched impact strength of 80PP/20PET reaches the maximum. However, further increase the compatibilizer to 12.5 phr, a significant increase of notched impact strength was observed. Therefore, the compatibilization strategy is based on the overall applicational requirement of PP/PET products. While the addition of too little SEBS-g-MA provides unsatisfactory product properties, the addition of an excess amount results in unnecessary costs due to high-priced SEBS-g- MA. The effect of reprocessing parameters includes extrusion and injection moulding temperatures on the mechanical properties of the reprocessed PP/PET blend were also investigated, with the PET as the minor phase. The results showed that low temperature reprocessing was effective in the maintenance of the original blends mechanical properties. With the addition of 15 phr SEBS-g-MA, the mechanical properties of PP/PET blend re-extruded and re-injection moulded at 195 oC and 220 oC could be maintained. This is attributed to the morphological maintenance of the PP/PET blend at low processing temperatures that keeps the PET phase is in its solid state. This analysis demonstrated that the process temperature optimization has the potential for maintaining the original mechanical properties of immiscible polymer blends during recycling