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Modelling the degradation processes in high-impact polystyrene during the first use and subsequent recycling
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.ORCID iD: 0000-0003-3572-7798
2007 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Polymers are subjected to physical and chemical changes during their processing, service life, and further recovery, and they may also interact with impurities that can alter their composition. These changes substantially modify the stabilisation mechanisms and mechanical properties of recycled polymers. Detailed knowledge about how the different stages of their life cycle affect the degree of degradation of polymeric materials is important when discussing their further waste recovery possibilities and the performance of recycled plastics. A dual-pronged experimental approach employing multiple processing and thermo-oxidation has been proposed to model the life cycle of recycled high-impact polystyrene (HIPS). Both reprocessing and thermo-oxidative degradation are responsible for coexistent physical and chemical effects (chain scission, crosslinking, apparition of oxidative moieties, polymeric chain rearrangements, and physical ageing) on the microstructure and morphology of polybutadiene (PB) and polystyrene (PS) phases; these effects ultimately influence the long-term stability, and the rheological and mechanical behaviour of HIPS. The PB phase has proved to be the initiation point of HIPS degradation throughout the life cycle. Thermo-oxidation seems to have more severe effects on HIPS properties; therefore, it can be concluded that previous service life may be the part of the life cycle with the greatest influence on the recycling possibilities and performance of HIPS recyclates in second-market applications. The results from the life cycle degradation simulation were compared with those obtained from real samples from a large-scale mechanical recycling plant. A combination of different analytical strategies (thermal analysis, vibrational spectroscopy, and chromatographic analysis) is necessary to obtain a detailed understanding of the quality of recycled HIPS as defined by three key properties: degree of mixing, degree of degradation, and presence of low molecular weight compounds.

Place, publisher, year, edition, pages
Stockholm: KTH , 2007. , 39 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2007:30
Keyword [en]
Recycling; high-impact polystyrene; degradation; quality analysis; thermal analysis; vibrational spectroscopy; chromatography techniques; thermo-oxidation; reprocessing; dynamic mechanical properties; polybutadiene microstructure.
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-4407ISBN: 978-91-7178-678-4 (print)OAI: oai:DiVA.org:kth-4407DiVA: diva2:12173
Presentation
2007-06-07, E2, Osquars backe 14, Stokcholm, 10:00
Opponent
Supervisors
Note
QC 20101119Available from: 2007-05-30 Created: 2007-05-30 Last updated: 2010-11-19Bibliographically approved
List of papers
1. Degradation of recycled high-impact polystyrene. Simulation by reprocessing and thermo-oxidation
Open this publication in new window or tab >>Degradation of recycled high-impact polystyrene. Simulation by reprocessing and thermo-oxidation
2006 (English)In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 91, no 9, 2163-2170 p.Article in journal (Refereed) Published
Abstract [en]

 A simulation of the degradation of high-impact polystyrene (HIPS), occurring during service life and mechanical recycling, was performed by multiple processing and thermo-oxidative ageing. All samples were characterized by differential scanning calorimetry (DSC), melt mass-flow rate (MFR) measurements, tensile testing and infrared spectroscopy (FTIR). Multiple processing and thermo-oxidative ageing clearly alter the oxidative stability and the elongation at break of the materials. These changes observed at a macroscopic scale have been related to chemical alterations in the structure of HIPS. The polybutadiene phase was demonstrated to be the initiation point of the degradative processes induced by processing, service life and mechanical recycling. Thermo-oxidative degradation affects more severely the degree of degradation of the material, so it may be deduced that the changes occurring during service life of HIPS are the part of the life cycle that mostly affects its further recycling possibilities and performance in second-market applications.

Keyword
recycling, degree of degradation, high-impact polystyrene, reprocessing, thermo-oxidation
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-7224 (URN)10.1016/j.polymdegradstab.2006.01.007 (DOI)000238918200031 ()2-s2.0-33744510923 (Scopus ID)
Note
QC 20100907Available from: 2007-05-30 Created: 2007-05-30 Last updated: 2017-12-14Bibliographically approved
2. Changes in the microstructure and morphology of high-impact polystyrene subjected to multiple processing and thermo-oxidative degradation
Open this publication in new window or tab >>Changes in the microstructure and morphology of high-impact polystyrene subjected to multiple processing and thermo-oxidative degradation
2007 (English)In: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 43, no 10, 4371-4381 p.Article in journal (Refereed) Published
Abstract [en]

Multiple processing and thermo-oxidation have been employed to simulate the degradative processes to which high-impact polystyrene (HIPS) is subjected during processing, service life, and mechanical recycling. A curve-fitting procedure has been proposed for the analysis of the individual bands corresponding to polybutadiene microstructure resulting from Raman spectroscopy. The analysis of the glass transition relaxations associated with the polybutadiene (PB) and polystyrene (PS) phases has been performed according to the free-volume theory. Both reprocessing and thermo-oxidative degradation are responsible for complex physical and chemical effects on the microstructure and morphology of PB and polystyrene PS phases, which ultimately affect the macroscopic performance of HIPS. Multiple processing affects PB microstructure and the free-volume parameter associated with the PS phase. Physical ageing of the PS phase predominates for shorter exposure to thermo-oxidation; after prolonged exposure, however, the chemical effects on the PB phase become significant and strongly influence the overall structure.

Keyword
high-impact polystyrene, degradation, Raman spectroscopy, dynamic-mechanical properties, polybutadiene microstructure
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-4891 (URN)10.1016/j.eurpolymj.2007.07.017 (DOI)000250386600031 ()2-s2.0-34748865085 (Scopus ID)
Note
QC 20100902Available from: 2008-09-17 Created: 2008-09-17 Last updated: 2017-12-13Bibliographically approved
3. Analytical strategies for the quality assessment of recycled high-impact polystyrene: A combination of thermal analysis, vibrational spectroscopy, and chromatography
Open this publication in new window or tab >>Analytical strategies for the quality assessment of recycled high-impact polystyrene: A combination of thermal analysis, vibrational spectroscopy, and chromatography
2007 (English)In: Analytica Chimica Acta, ISSN 0003-2670, E-ISSN 1873-4324, Vol. 604, no 1, 18-28 p.Article in journal (Refereed) Published
Abstract [en]

Various analytical techniques (thermal analysis, vibrational spectroscopy, and chromatographic analysis) were used in order to monitor the changes in polymeric properties of recycled high-impact polystyrene (HIPS) throughout mechanical recycling processes. Three key quality properties were defined and analysed; these were the degree of mixing (composition), the degree of degradation, and the presence of low molecular weight compounds. Polymeric contaminations of polyethylene (PE) and polypropylene (PP) were detected in some samples using differential scanning calorimetry (DSC). Vibrational spectroscopy showed the presence of oxidised parts of the polymeric chain and gave also an assessment of the microstructure of the polybutadiene phase in HIPS. The presence of low molecular weight compounds in the HIPS samples was demonstrated using microwave assisted extraction followed by gas chromatography mass spectrometry (GC-MS). Several volatile organic compounds (VOCs), residues from the polymerisation, additives, and contaminations were detected in the polymeric materials. Styrene was identified already in virgin HIPS; in addition, benzaldehyde, alpha-methylbenzenaldehyde, and acetophenone were detected in recycled HIPS. The presence of oxygenated derivates of styrene may be attributed to the oxidation of polystyrene (PS). Several styrene dimers were found in virgin and recycled HIPS; these are produced during polymerisation of styrene and retained in the polymeric matrix as polymerisation residues. The amount of these dimers was highest in virgin HIPS, which indicated that emission of these compounds may have occurred during the first lifetime of the products. This paper demonstrates that a combination of different analytical strategies is necessary to obtain a detailed understanding of the quality of recycled HIPS.

Keyword
recycling, quality analysis, high-impact polystyrene, degradation, thermal analysis, vibrational spectroscopy, chromatographic techniques
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-4892 (URN)10.1016/j.aca.2007.04.046 (DOI)000251293700004 ()2-s2.0-35648936956 (Scopus ID)
Note
QC 20100920Available from: 2008-09-17 Created: 2008-09-17 Last updated: 2017-12-13Bibliographically approved

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