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Thermally Expandable Microspheres with Excellent Expansion Characteristics at High Temperature
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.ORCID iD: 0000-0002-8348-2273
2010 (English)In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 117, no 1, 384-392 p.Article in journal (Refereed) Published
Abstract [en]

Thermally expandable core/shell particles with a poly(acrylonitrile-co- methacrylonitrile) shell and a hydrocarbon core (blowing agent) have been prepared by suspension polymerization. The objective of this study was to gain a deeper understanding of the parameters determining the expansion properties of these microspheres. It was found that the amount, the boiling point, and the structure of the blowing agent are important parameters for the expansion properties. For example, a higher maximum expansion was reached when using bulkier blowing agents and thus a lower diffusion rate through the polymer shell. Further, the amount and structure of the crosslinker were also found to be essential for the expansion properties. For this particular system, it was found that a dimethacrylate-functional crosslinker gave significantly better expansion when compared with diacrylate-or divinylether-based crosslinkers. Beside these parameters, it was also observed that the particle-size distribution influence the expansion properties of the microspheres.

Place, publisher, year, edition, pages
2010. Vol. 117, no 1, 384-392 p.
Keyword [en]
Blowing agents, Coreshell polymers, Crosslinking, Radical polymerization
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-11977DOI: 10.1002/app.31543ISI: 000277523500047Scopus ID: 2-s2.0-77950936660OAI: oai:DiVA.org:kth-11977DiVA: diva2:291728
Note
QC 20101022. Uppdaterad från Accepted till Published (20101022).Available from: 2010-02-03 Created: 2010-02-03 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Thermally Expandable Microspheres Prepared via Suspension Polymerization - Synthesis, Characterization, and Application
Open this publication in new window or tab >>Thermally Expandable Microspheres Prepared via Suspension Polymerization - Synthesis, Characterization, and Application
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Thermally expandable microspheres are polymeric core/shell particles in which a volatile hydrocarbon is encapsulated by a thermoplastic shell. When these microspheres are heated, they expand and increase their volume dramatically. This volume increase is retained upon cooling, leading to a density reduction from around 1100 kg m-3 to about 30 kg m-3. Since the development in the early 1970´s, microspheres have been used extensively by the industry as a foaming agent or light weight filler.

In this thesis, microspheres with a poly(acrylonitrile-co-methacrylonitrile) shell have been synthesized through free radical suspension polymerization. The microspheres have been characterized with respect to particle morphology and expansion properties in order to deepen the understanding of the microspheres.

It was found that the monomer feed ratio and the polymerization temperature are very important parameters with respect to the expansion properties. Excellent expansion could only be accomplished when polymerizing at 62 °C, with the acrylonitrile feed, fAN, being around 60 mol%, even though core/shell microspheres are formed over a much wider range of fAN. Furthermore, no expansion was achieved when polymerizing at 80 °C, even though no noticeable differences were found, compared to the corresponding sample polymerized at 62 °C.

It was also shown that the expansion properties can be modified by replacing the encapsulated hydrocarbon by another hydrocarbon with a different boiling point. Not only is the boiling point important, the structure of the hydrocarbon is also important. Isooctane which is highly branched was found to give superior expansion compared to linear or cyclic hydrocarbons having a similar boiling point.

Crosslinking of the polymer shell has proven to be very important for the expansion properties. Both the amount and the structure of the crosslinker are important parameters. Especially the maximum expansion can be improved by the crosslinking of the polymer shell. This originates in an increase in the shape persistence of the expanded microspheres at elevated temperatures. By the combination of crosslinkers that are incorporated separately into the polymer shell, the onset temperature of expansion can be increased significantly.

Finally, the surface of microspheres has been modified by grafting poly(glycidyl methacrylate) from the surface by ARGET ATRP. Given that the reaction conditions are appropriate, such modifications can be performed with only limited effects on the expansion properties of the microspheres.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. 54 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2010:4
Keyword
Thermally expandable microspheres
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-11981 (URN)978-91-7415-542-6 (ISBN)
Public defence
2010-02-26, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2010-02-04 Created: 2010-02-03 Last updated: 2010-04-28

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Malmström, Eva

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