Modification of polymer properties using nanofillers

Much research is being done to develop effective material combinations of polymer nanocomposites with tailored properties. Commercial products such as automotive parts, sporting goods, and packaging materials are already available that make use of nano-sized fillers. Typically, the mechanical, barrier, and fire performance of polymer nanocomposites is better to that of traditional microcomposites. Because nanocomposites require significantly less filler material, the melt-compounding is easier and the final products made from them are lighter in weight.

In industrial high-volume applications, melt-compounding is considered the most convenient and preferred method to incorporate micro- and nanofiller powders in a thermoplastic matrix. “However, it is very difficult to uniformly disperse nanofillers, and in many cases the nanofiller dispersion is not sufficient,” says Lic. Tech. Katja Nevalainen, whose doctoral dissertation will be publicly examined at Tampere University of Technology on Friday, 5 April, 2013.

The slow progress in commercialization of polymer nanocomposites is mainly due to their limited performance resulting from poor bonding between filler and matrix and from nanofillers’ tendency to agglomerate. In addition, there is growing concern about the health and environmental effects of nanofillers. By atomic-layer deposition (ALD), it is possible to create very thin nanofiller layers directly on micron-sized polymer particles before melt-compounding. Subsequent melt-compounding of such ALD-coated polymer particles is seen as an attractive method for producing metal oxide nanocomposites, as it improves nanofiller dispersion.

Nevalainen studied the effect of the processing method on nanofiller dispersion and the properties of a variety of nanofilled matrixes. Nevalainen’s findings showed enhanced mechanical and fire properties for conventionally melt-compounded composites compared to their unfilled counterparts, especially polycarbonate nanoclay composites and polypropylene multi-walled carbon nanotube composites, respectively. The potential of nanofillers with a large surface area to improve composite properties was not, however, fully realized. In addition to individual non-agglomerated fillers, micron-sized filler clusters, stacks, or bundles were found in the composite depending on the incorporated filler.

Well-dispersed and agglomerate-free nanocomposites were obtained by melt-compounding ALD-coated polymer particles. Application of ALD-tailored melt-compounding enables formation of ribbon- or plate-like nanofillers with a high aspect ratio. Such filler morphology is considered useful especially for mechanical reinforcement.  However, incorporation of individually dispersed nanofillers with a high aspect ratio in a polymer matrix does not necessarily guarantee enhanced composite properties. The effect of ALD-created metal oxide nanofillers was modest if significant polymer degradation could be avoided. A finding mainly attributed to low filler content and possible insufficient interaction between filler and polymer. Though only minor changes were detected in the mechanical properties, ALD-tailored melt-compounding is still considered an attractive technology to fabricate agglomerate-free nanocomposites. A further understanding and fine-tuning of the ALD process is required to realize the potential of this processing approach.

Public defence of a doctoral dissertation on Friday, 5 April

The doctoral dissertation of Lic. Tech. Katja Nevalainen in the field of materials technology ”Melt-Compounded Composites of Inorganic Nanofiller and Atomic-Layer-Deposition-Coated Polymer Powder” will be publicly examined at the Faculty of Engineering Sciences of Tampere University of Technology (TUT) in room K1702, in the Konetalo building (Korkeakoulunkatu 6, Tampere, Finland) on 5.4.2013 at 12:00.

The opponents will be Professor Luigi Torre (University of Perugia, Italy) and Professor Carl-Eric Wilén (Åbo Akademi University, Finland). Professor Jyrki Vuorinen from TUT’s Department of Materials Science will act as Chairman.

Katja Nevalainen (34) comes from Jämsänkoski, and she has been working several years as a researcher at the Department of Materials Science, TUT.

Further information: Katja Nevalainen, katja.nevalainen@tut.fi