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Long-term Properties of Sustainable Polymeric Materials: Mechanical Recycling and Use of Renewable Resources
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.ORCID iD: 0000-0002-2139-7460
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.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2009:44
Keyword [en]
Sustainable materials, mechanical recycling, polyolefin, reprocessing, accelerated ageing, chromatography, biofilm, microenvironment chamber, environmental degradation, biocomposite, nanocomposite
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-10934ISBN: 978-91-7415-402-3 (print)OAI: oai:DiVA.org:kth-10934DiVA: diva2:232730
Public defence
2009-09-17, F3, KTH, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100811Available from: 2009-09-03 Created: 2009-08-25 Last updated: 2010-08-11Bibliographically approved
List of papers
1. The Design of a Test Protocol to Model the Degradation of Polyolefins During Recycling and Service Life
Open this publication in new window or tab >>The Design of a Test Protocol to Model the Degradation of Polyolefins During Recycling and Service Life
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.

Keyword
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
Identifiers
urn:nbn:se:kth:diva-18246 (URN)10.1002/app.29724 (DOI)000264247300087 ()2-s2.0-64249105217 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
2. Comparison of extraction methods for sampling of low molecular compounds in polymers degraded during recycling
Open this publication in new window or tab >>Comparison of extraction methods for sampling of low molecular compounds in polymers degraded during recycling
2008 (English)In: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 44, no 6, 1583-1593 p.Article, review/survey (Refereed) Published
Abstract [en]

The demand for mechanical recycling of plastic waste results in an increasing amount of recycled polymeric materials available for development of new products. In order for recycled materials to find their way into the material market, high quality is demanded. Thereby, a complete and closed loop of polymeric materials can be achieved successfully. The concept of high quality for recycled plastics imply that besides a pure fraction of e.g. polyethylene (PE) or polypropylene (PP), containing only minor trace amount of foreign plastics, knowledge is required about the type and amount of low molecular weight (LMW) compounds. During long-term use (service-life), products made of polymeric materials will undergo an often very slow degradation where a series of degradation products are formed, in parallel, additives incorporated in the matrix may also degrade. These compounds migrate at various rates to the surrounding environment. The release rate of LMW products from plastics depends on the initiation time of degradation and the degradation mechanisms. For polymers the formation of degradation products may be initiated already during processing, and subsequent use will add products coming from the surrounding environment, e.g. fragrance and aroma compounds from packaging. During recycling of plastics, emissions which contain a series of different LMW compounds may reach the environment leading to unwanted exposure to additives and their degradation residues as well as degradation products of polymers. Several extraction techniques are available for sampling of LMW compounds in polymers before chromatographic analysis. This paper reviews and compares polymer dissolution, accelerated solvent extraction (ASE), microwave assisted extraction (MAE), ultrasound assisted extraction (UAE), super critical fluid extraction (SFE), soxhlet extraction, head-space extraction (HS), head-space solid phase micro extraction (HS-SPME), and head-space stir bar sorptive extraction (HSSE) as appropriate sampling methods for LMW compounds in recycled polymers. Appropriate internal standards useful for these kinds of matrices were selected, which improved the possibility for later quantification. Based on the review of extraction methods, the most promising techniques were tested with industrially recycled samples of HDPE and PP and virgin HDPE and PP for method comparison.

Keyword
extraction, recycled polymers, accelerated solvent extraction (ASE), microwave assisted extraction (MAE), head-space solid phase micro, extraction (HS-SPME), head-space stir bar sorptive extraction (HSSE), supercritical-fluid extraction, microwave-assisted extraction, solid-phase microextraction, performance liquid-chromatography, soxhlet, extraction, solvent-extraction, gas-chromatography, additives, polypropylene, polyethylene
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-17686 (URN)10.1016/j.eurpolymj.2008.03.027 (DOI)000257619000001 ()2-s2.0-44649086397 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
3. Identification of degadation products and additives using microwave assisted extraction (MAE) and Gas Chromatography-Mass Spactrometry(GC-MS) in polyolefins subjected to controlled recycling and thermal ageing
Open this publication in new window or tab >>Identification of degadation products and additives using microwave assisted extraction (MAE) and Gas Chromatography-Mass Spactrometry(GC-MS) in polyolefins subjected to controlled recycling and thermal ageing
(English)Manuscript (preprint) (Other academic)
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-24029 (URN)
Note
QC 20100811Available from: 2010-08-11 Created: 2010-08-11 Last updated: 2010-08-11Bibliographically approved
4. Microbiological growth testing of polymeric materials: an evaluation of new methods
Open this publication in new window or tab >>Microbiological growth testing of polymeric materials: an evaluation of new methods
2005 (English)In: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 24, no 5, 557-563 p.Article in journal (Refereed) Published
Abstract [en]

Biofilms growing on high voltage insulators made of silicone rubber cause changes in appearance and properties of the silicone material. This study presents the design and building of microenvironment chambers simulating outdoor environment and the use of these for long-term studies of the development of mixed biofilms on silicone rubber materials. Results from the microenvironment chambers are compared to standard test procedures used in combination with new methods to evaluate the effect of two common flame retardants, ATH and zinc borate, on the development of a biofilm. Algae, bacteria and fungi isolated from silicone rubber insulators collected from Tanzania, Sri Lanka and Sweden, respectively, were used in the tests performed. Results show that zinc borate has a protective effect against all the microorganisms tested.

Keyword
Algae; Biofilm; Fungi; Insulators; Silicone rubber; Zinc borate
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-5034 (URN)10.1016/j.polymertesting.2005.02.005 (DOI)000229979000004 ()2-s2.0-19144366150 (Scopus ID)
Note
QC 20100811Available from: 2005-04-18 Created: 2005-04-18 Last updated: 2017-12-05Bibliographically approved
5. The effect of biodegradation on surface and bulk property changes of polypropylene, recycled polypropylene and polylactide biocomposites
Open this publication in new window or tab >>The effect of biodegradation on surface and bulk property changes of polypropylene, recycled polypropylene and polylactide biocomposites
2009 (English)In: International Biodeterioration & Biodegradation, ISSN 0964-8305, E-ISSN 1879-0208, Vol. 63, no 8, 1045-1053 p.Article in journal (Refereed) Published
Abstract [en]

Biocomposites were subject to exposure to a mixture of fungi and algae in a microenvironment chamber. Surface and bulk property changes of polypropylene/wood flour, recycled polypropylene/cellulose and polylactide/wood flour were monitored by tensile testing, Differential Scanning Calorimetry (DSC), Thermal Gravimetric Analysis (TGA) and Field Emission Scanning Electron Microscope (FE-SEM). All the biocomposites showed a substantial decrease in toughness after 28 and 56 days of hydrolysis. The ductility increased after 28 and 56 days, but deteriorated after 84 days of hydrolysis. Biofilm formation occurred on all biocomposites even if the polymer itself was inert to biodegradation. The microbial colonization affected mainly the surface properties of polypropylene biocomposites while changes were monitored also in the bulk properties of polylactide biocomposites. The cellulose fibres in the composites gave a more easily colonized surface mainly attributed to water uptake. In the short term perspective, the water uptake offered better conditions for biofilm adhesion, and in the longer perspective the exposure to microorganisms also resulted in mechanical degradation, followed by biodegradation of cellulose. With time this will leave a porous matrix of polypropylene, while biodegradable polymers such as polylactide will degrade in parallel with the fibre part.

Keyword
Biofilm, Biocomposites, Hydrolysis, Biodegradation, Material properties, mechanical-properties, polymeric materials, composites, fibers, cellulose, wood, degradation, absorption, moisture, biofilms
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-19000 (URN)10.1016/j.ibiod.2009.08.003 (DOI)000272218800013 ()2-s2.0-71849084138 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
6. Environmental degradation of PP-montmorillonite nanocomposites by thermo-oxidation, day-light photo-oxidation and exposure to soil.
Open this publication in new window or tab >>Environmental degradation of PP-montmorillonite nanocomposites by thermo-oxidation, day-light photo-oxidation and exposure to soil.
(English)Manuscript (preprint) (Other academic)
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-24033 (URN)
Note
QC 20100811Available from: 2010-08-11 Created: 2010-08-11 Last updated: 2010-08-11Bibliographically approved

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