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The Design of a Test Protocol to Model the Degradation of Polyolefins During Recycling and Service Life
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.ORCID iD: 0000-0002-2139-7460
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.ORCID iD: 0000-0002-5394-7850
2009 (English)In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 112, no 3, 1835-1844 p.Article in journal (Refereed) Published
Abstract [en]

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 thermo-oxidation. 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 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.

Place, publisher, year, edition, pages
2009. Vol. 112, no 3, 1835-1844 p.
Keyword [en]
degradation, injection molding, polyolefins, recycling, structure-property relations, high-density polyethylene, thermooxidative degradation, multiple, extrusions, thermal-oxidation, solid-state, polypropylene, waste, stability, energy, impact
National Category
Polymer Chemistry
URN: urn:nbn:se:kth:diva-18246DOI: 10.1002/app.29724ISI: 000264247300087ScopusID: 2-s2.0-64249105217OAI: diva2:336292
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2011-01-14Bibliographically approved
In thesis
1. Long-term Properties of Sustainable Polymeric Materials: Mechanical Recycling and Use of Renewable Resources
Open this publication in new window or tab >>Long-term Properties of Sustainable Polymeric Materials: Mechanical Recycling and Use of Renewable Resources
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

New strategies for management of the accumulating amounts of plastic waste are required, to achieve a sustainable development in terms of material production and use. After service life, the materials should be recovered and recycled efficiently to provide a valuable resource for future applications. Optimised use of amended recycled polymeric materials, e.g. reinforced with natural fibres, and polymers from renewable resources give rise to polymeric materials with lower environmental impact. The recovery of plastic waste by means of mechanical recycling is a favourable route for preservation of raw materials and energy. Deficient knowledge about the overall quality of the recyclates, such as the degree of degradation, mixing and contamination, has resulted in restricted subsequent application of the recycled materials. Therefore, quality assessment of the recycled polymers is required for guaranteed performance in future applications.

Recycling and service life of polyolefins (PP and HDPE) were modelled by multiple reprocessing and thermo-oxidation. The material properties of the polyolefins were affected by both thermo-oxidation and thermo-mechanical degradation. PP showed higher susceptibility to reprocessing and elevated formation of low molecular weight compounds compared to HDPE. Release of the compounds during service life is anticipated on account of the extensive migration of these volatiles during thermal ageing.

Microenvironment chambers simulating outdoor environmental conditions were designed to monitor biofilm formation on silicon rubber composite materials. Furthermore, the microenvironments were successfully used to determine the long-term properties of biocomposites, consisting of conventional or biodegradable polymeric matrices and natural fibres as reinforcement, by subjecting the materials to a hydrolytic environment and microbiological degradation. Facilitated surface colonisation due to the presence of cellulose fibres in the composites was mainly attributed to water uptake. Biodegradation of PP biocomposites influenced mainly the surface properties whereas for PLA the bulk properties were also highly affected.

PP-clay nanocomposites were subjected to simulated environmental degradation by thermo-oxidation, daylight photo-oxidation and exposure to forest soil. Increased crystallinity and surface oxidation were detected after thermo-oxidation of the materials. The presence of clay promoted formation of carbonyl compounds during photo-oxidation and water uptake during exposure to soil.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. 62 p.
Trita-CHE-Report, ISSN 1654-1081 ; 2009:44
Sustainable materials, mechanical recycling, polyolefin, reprocessing, accelerated ageing, chromatography, biofilm, microenvironment chamber, environmental degradation, biocomposite, nanocomposite
National Category
Polymer Chemistry
urn:nbn:se:kth:diva-10934 (URN)978-91-7415-402-3 (ISBN)
Public defence
2009-09-17, F3, KTH, Lindstedtsvägen 26, Stockholm, 10:00 (English)
QC 20100811Available from: 2009-09-03 Created: 2009-08-25 Last updated: 2010-08-11Bibliographically approved

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