Characterization of VOCs and additives in Italian PET bottles and studies on potential functional aldehydes scavengers

This study focused on characterization of Volatile Organic Compounds (VOCs) as contaminants and non-volatile additives in Italian PET bottles, also suggesting potential functional aldehydes scavengers. Several VOCs, such as acetic aldehyde (AA), butanal, 3-methyl butanal, 1,3-dioxolane, pentanal, hexanal, octanal, 5-hepten-2-one, nonanal, and decanal, were identified by Head Space-Gas Chromatography/Mass Spectrometry (HS-GC/MS) in the PET bottles used for the packaging of six Italian brands mineral waters. AA, 1,3-dioxolane, octanal, 5-hepten-2-one, nonanal, and decanal were the most abundant compounds identified. These contaminants were also identified in the PET-bottled mineral waters. Different experiments using bottle-grade PET pellets (Btlg-PET) and PET bottles’ fragments with and without the addition of epoxidized soybean oil (ESBO) or erucamide as lubricant/plasticizer additives, poly(m-xylene adipamide) (MXD6), and/or anthranilamide (2-aminobenzamide) as potential aldehydes scavengers were carried out. Mostly VOCs observed in the PET bottles analysed were identified in a neat ESBO sample. The presence of the ESBO additive in the PET-bottle fragments was also observed by matrix-assisted laser desorption/ionization time of flight mass spectrometry analysis (MALDI–TOF MS). The ESBO sub-products were not observed in the virgin btlg-PET pellets analysed by both HS-GC/MS and MALDI–TOF MS. These results suggest that the VOCs come from an ESBO additive probably loaded during the blow-moulding processes used for the manufacturing of PET bottles. Further studies established that MXD6 (1%w), an efficient oxygen scavenger, could be also used as AA scavenger even in the presence of the commonly used anthranilamide.

Morphology optimization of poly(ethylene terephthalate)/polyamide blends compatibilized via extension-dominated twin-screw extrusion

Poly(ethylene terephthalate) (PET) and polyamide (PA) are immiscible polymers, which requires the use of compatibilizers to stabilize the morphology and achieve acceptable property levels. Therefore, controlling the degree of dispersion, especially the size of the disperse PA droplets in the PET matrix is of paramount importance. This study aims to improve the mixing, i.e., minimize PA droplet size, in immiscible and compatibilized PET/PA and PET/Nylon-MXD6 (MXD6) blends by resorting to extension-dominated mixing in twin-screw extrusion (TSE). MXD6 is an aromatic polyamide similar in polarity to PET, so it is expected that it will blend more effectively than is the case with aliphatic nylon-6 and PET. Two screw configurations are used, a benchmark shear-dominated screw with kneading blocks (KBs) in an aggressive configuration, and an extension-dominated screw configuration with static mixers with hyperbolic C–D channels, recently developed by our group, in place of the KBs. The results show that the use of extensional mixing elements (EMEs) in place of KBs results in a significant decrease of both average and maximum droplet size for all blends, and up to more than one order of magnitude between the most extreme cases of the KB-processed immiscible blend and EME-processed compatibilized blends.

Analysis of Models Predicting Morphology Transitions in Reactive Twin-Screw Extrusion of Bio-Based Polyester/Polyamide Blends

Immiscible PLA/PA11 of 80/20 and 50/50 wt% were compatibilized through addition of p-toluenesulfonic acid (TsOH) catalyst in reactive ultra-high speed twin-screw extrusion. Two mixing screw designs were compared for their ability to disperse the PA11 droplets in the PLA matrix as a function of screw speed up to 2000 rpm. The size and polydispersity of droplets of dispersed PA11 decreased when a high shear (HS) screw was used, whereas broad droplet size distribution was produced in the low shear (LS) screw. Two models predicting the droplet size dependence on shear rate, viscosity ratio and interfacial tension were fit to the experimental data. The Serpe model including volume fraction effects produced a better fit compared to the Wu model, which does not include volume fraction effects. Mechanical testing indicated that the compatibility of PLA/PA11 blends was improved through addition of TsOH catalyst for 50/50 wt% blends due to ester – amide exchange reactions at the interfaces in the immiscible PLA and PA11 phases. The enhancement of ductility was greater after processing with the LS screw configuration than the HS screw configuration. The inferior properties after high shear mixing were likely due to molecular weight degradation during processing. While the aggressive shear in the HS screw design resulted in fine dispersion, care should be taken to minimize degradation, especially for shear sensitive polymers.