The design of a test protocol to model the degradation of polyolefins during recycling and service life

Abstract

In terms of the sustainable development for polymeric materials the recovery of plastic waste by means of mechanical recycling is a favorable technique. The largest part of the collected plastic municipal solid waste fraction consists of packaging materials, e.g., polypropylene (PP) and polyethylene. A major drawback to the increased use of recycled polymers is the lack of knowledge about the property changes and the overall quality of the recyclates, e.g., the degree of degradation, mixing, and contamination. This article presents a test protocol for description of the mechanical, physical, and chemical property changes during recycling and service life by combining several reprocessing cycles and thermooxidation. The test protocol was designed to mimic the degradation mechanisms potentially occurring in the materials during the service life and the reprocessing. Virgin PP and HDPE were multiply processed by injection molding. Service life of plastic materials was modeled by accelerated thermal degradation of one time processed materials. Tensile testing, MFR, HT-SEC, DSC, FTIR, and SEM were used to analyze material changes. In parallel, a set of industrially recycled PP and HDPE were also subjected to the same analyses. The results proved that recycled plastics maintain the majority of the material properties even when reprocessed several times. It was demonstrated that the mechanical and thermal properties of PP and HDPE were preserved also after several reprocessing steps. Initiation of degradation was observed for PP but not for HDPE. A decrease in M w of PP from 240,000 to 190,000 (six times reprocessed) was established, this corresponds to an increase in MFR from 8 to 18 g/10 min. By FTIR, it was shown that the carbonyl index increased. The loss of stabilizers affects the properties of the final product. In comparison, industrially recycled PP and HDPE presented to some extent poorer mechanical properties than the materials subjected to model recycling.

The Effect of Multiple Extrusions on the Properties of Montmorillonite Filled Polypropylene

“…Apparently, this does not lead to a decrease in mechanical properties. This has also been observed by Stromberg and Karlsson [30], and could be attributed to the presence of stabilizers in commercial polypropylenes. The other important tensile properties are presented in Table 2.…”

Formulation and processing of virgin and recycled polyolefin/oil blends for the development of lubricating greases

“…The band at 1600 cm À1 has been previously related to part of the ketone group [-C5 5C-C5 5O] [29,30]. On the other hand, the peak at 1590 cm À1 can be attributed to carboxylic groups which may arise from the degradation of polyolefins [31]. These results suggest that, in order to obtain a material with suitable rheological characteristics, the mixing time should be as short as possible whilst ensuring a sufficiently homogeneous mixture (60 min).…”

Dielectric spectroscopy of recycled polylactide

“…Among all material recovery methods [4], mechanical recycling represents one of the most successful processes, although during reprocessing, polymers are subjected to the influence of several degrading agents that may modify the structure [5] and consequently change their long-term properties [6][7][8][9][10][11].…”