Effects of Hygrothermal Treatment


The amount of waste from post-consumer poly(ethylene terephthalate) (PET) and polypropylene (PP) especially in the packaging industry encouraged an investigation to produce innovative new products from recycled PET (RPET) and recycled PP (RPP) for application in the composite and synthetic fibre industries.

This research investigates ways to reutilise and upgrade materials recovered from post-consumer plastic bottles. The RPET and RPP flakes supplied by Yasuda-Sangyo Co. Ltd. were recovered from post-consumer waste drinking bottles in Japan. The RPET and RPP were mechanically blended at ratios of 95/5 and 90/10, chosen to emulate the actual bottle/cap weight ratios of 2-litre and 500 ml drinking bottle.

The RPET/RPP blends were then subjected to hygrothermal treatment in water bath up to four weeks at below transition glass temperature to determine the amount of moisture absorption. At predetermined time intervals, the pellets were removed from the water-aging chamber, quickly wiped-dry and weighed at various intervals to determine their water uptake and evaluated their mechanical performance.

Investigation of the RPET/RPP blend indicated that the addition of compatibilizer increased the compatibility between the RPET and RPP phases. This increased the toughness and deformability properties of the blends even with low compatibilizer content. While the addition of compatibilizer enhances the mechanical properties of RPET/RPP blends, the overloading of compatibilizers would weaken the RPET/RPP interface when exposed to moisture and heat. This could suggest that the compatibilizers are mostly concentrated at the interfacial regions of the blends to form an interface, as shown by the hygrothermal treatment process.

The moisture absorption capability of RPET/RPP pellets increased when the compatibilizer content was increased. The hygroscopic nature of the compatibilizer increases water absorption capability of the blends, which could cause significant deterioration in the mechanical performance. Water absorption rate was higher when higher compatibilizer content was present in the RPET/RPP blend resulting into a significant decline in tensile strength. A ductile to brittle failure mode was observed in most specimens, which is attributed to the reduction in RPET-RPP interfacial strength. This suggests that the compatibilizers were mostly present at the interface between RPET and RPP phases to form a region that is sensitive to both moisture and heat. Water absorption indicates that the hygroscopic nature of the compatibilizer increases the water absorption capability.

The morphology of pellets has been shown to have a profound effect on the properties of injection mouldings. Research work on the morphology development of PP dispersed phase and the difference of crystalline distribution of the RPET/RPP blends along the extrusion line prior to pelletizing is being initiated. The effect of compatibilizer content will be correlated to the growth rate of PP phase and different crystallization rate of the different RPET/RPP blends.

Contact information:

Siti Fatimah Aminuddin (This email address is being protected from spambots. You need JavaScript enabled to view it.)
Centre of Foundation Studies
Universiti Teknologi MARA

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