Measurement of peroxides in the volatile degradation products of polypropylene photooxidation

Thermal Analysis of Plastics Used in the Food Industry

Fires in landfills, where used plastic packaging waste is discarded, have shown how great a fire hazard these types of materials pose. In this study, the course of thermo-oxidation of samples made of polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET) based plastics was determined. Based on an analysis of the dissociation energy of bonds between atoms in a polymer molecule, the mechanisms responsible for the character and course of degradation were observed. It was found that the degradation rate of PP and PS could be a result of the stability of C-H bonds on the tertiary carbon atom. In the case of PS, due to facilitated intramolecular hydrogen transfer, stabilization of hydroperoxide, and formation of a stable tertiary alcohol molecule, the onset of degradation is shifted towards higher temperatures than in the case of PP. Notably, the PP fragmentation occurs to a greater extent due to the easier course of β-scission. In addition, it was found that during a fire, the least amount of heat would be generated by thermo-oxidation of PS-based plastics. This is a result of the formation of a styrene molecule during decomposition that, due to the high stability of bonds in the aromatic ring, escapes from the combustion zone without oxidation. It has been proven that the greatest thermal effect accompanies PET decomposition, during which a phenyl radical is produced, where the C-H bonds break more easily in comparison with the bonds of an intact ring.

Formation and Emissions of Volatile Organic Compounds from Homo-PP and Co-PP Resins during Manufacturing Process and Accelerated Photoaging Degradation

Volatile organic compounds (VOCs) from polypropylene (PP) seriously restricts the application of PP in an automotive field. Herein, the traceability of VOCs from PP resins during manufacturing process and accelerated photoaging degradation was clarified on basis of an accurate characterization method of key VOCs. The influence of PP structures on changing the accelerated photoaging degradation on the VOCs was systematic. The VOCs were identified by means of Gas chromatography (GC) coupled with both a hydrogen flame ion detector (FID) and a mass spectrometry detector (MSD). Results showed that both the molecular structure of PP and the manufacturing process affected the species and contents of VOCs. In addition, the photoaging degradation of PP resulted in a large number of new emerged volatile carbonyl compounds. Our work proposed a possible VOC formation mechanism during the manufacturing and photoaging process. VOCs from PP resins were originated from oligomers and chain random scission during thermomechanical degradation. However, β scission of alkoxy radical and Norrish tape I reactions of ketones via intermediate transition were probably the main VOCs formation routes towards PP during photoaging degradation. This work could provide scientific knowledge on both the accurate traceability of VOCs emissions and new technology for development of low-VOCs PP composites for vehicle.

Photo-Degradation of Polypropylene-Ascorbic Acid TiO2 Composite Films

The surface modification of titanium dioxide (TiO2), which can be easily attained by a simple addition of ascorbic acid (AA) to aqueous TiO2 suspensions, affects the photodegradation. Surface modification results in the formation of a colored surface complex that causes red shift in the absorption threshold of TiO2. Photodegradable polypropylene (PP) composite films were prepared by embedding AA modified nano TiO2 into the PP matrix (PP/(AA/TiO2)). The photocatalytic degradation behavior of PP/(AA/TiO2) composite film under UV light irradiation as investigated and compared with those of the PP/TiO2 and neat PP films, with the aid of UV-Vis spectroscopy, Fourier Transform Infrared spectroscopy, weight loss monitoring, tensile test and scanning electron microscopy. The degradation rate of the PP/(AA/TiO2) composite films is three times higher than that of PP/TiO2 film and six times higher than that of neat PP film. In addition, the FTIR spectra show that the intensity of the peak of carbonyl group for neat PP is much lower than that of the composite film.