The Role of Residual Contaminants and Recycling Steps on Rheological Properties of Recycled Polypropylene

Abstract

Recycling of polymers is one of the alternatives to reduce the impact of polymers presence on the environmental. However, the contaminants, defined as non-intentionally added substances, present in recycled material may migrate into food and also change its molecular structure. This work addresses the extractability/migration of contaminants from polypropylene (PP) samples into food simulants and the influence of these contaminants on the molecular structure of recycled PP. For this PP was contaminated with several substances to simulate a "worst-case" scenario and, then it was submitted to a recycling process. Extractability tests were performed by solid-phase microextraction and gas chromatography coupled to mass spectroscopy both to evaluate the presence of contaminants in the PP samples and their ability to migrate in food simulants. Additionally, molecular changes of the PP samples were evaluated by oscillatory rheometry. After washing and extrusion of the PP samples the extractability results showed considerable reductions of migrations in the food simulants and indicated, in some cases, compliance with regulations for using recycled polymer in contact with food. The residual contaminants were present in the polymer, the high temperatures and shear rates play an important role in molecular changes. Finally, the results highlight the importance of the use of rheological measurements to detect the influence of contaminants in recycled materials. Their presence result in material with different molar mass, that may be applied in different market applications.

Assessment of the Impact of Superficial Contamination and Thermo-Oxidative Degradation on the Properties of Post-Consumer Recycled Polypropylene

“…This result highlights the necessity of adding antioxidants to compensate, to some extent, for the deterioration of the post-consumer recycled plastics properties. As can be seen from Table 4 , the oxidation induction times of all the recycled PP samples vary between 41.6 and 61.4 s. The latter time is the best performance shown by rPPhwca samples with the most thorough hot-washing treatment with cleaning agents, corroborating various researchers’ conclusions [ 27 , 29 , 41 ] about the accelerating effect of thermo-oxidative degradation due to the presence of contaminants. Besides the antioxidant’s destruction and influence of the particulate contaminants, which cannot be entirely removed by washing, the concentration, and composition of residual polymerization catalysts and metal additives may contribute to the formation of degradation products and, thus, decrease the thermo-oxidative stability of PP [ 42 ].…”

Effect of Virgin PP Substitution with Recycled Plastic Caps in the Manufacture of a Product for the Telephony Sector

“…Mechanical recycling is the most common way of reusing post-consumer plastic caps [11], mainly because of the overall efficiency of the process [12]. Nevertheless, recycling systems should be designed considering each material's degradation mechanisms [13]. For PP and HDPE, this occurs due to successive recycling or exposure to solar radiation that causes scissions in the polymeric chains [14,15] and weakens their mechanical properties [16][17][18].…”