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232 9 Environment-Friendly Methods for Converting Biodegradable Polyesters

in industry, as starting materials for SPCs, as carriers for controlled drug delivery,
and others. In this way, it is possible to convert any bulk polymer into nano-sized
material. Recently, this approach was essentially improved by excluding the use
of organic solvents – the only solvent used is water. It this way, the method
became environmentally friendly, cost effective (the water-soluble polymer can
be regenerated and reused for the same purpose), and, last but not the least, the
final nano-particles became more attractive for biomedical applications.
Further development of the same method was the finding that the final nano-
morphology, being of two basic types, can be controlled. If hydrogen bonding
between the blend partners is missing, the observed morphology is of individual
not interconnected nanofibrils. In case hydrogen bonds are present, the nano-
morphology represents a nanofibrillar nanoporous 3-D network. In this way, using
hydrogen bonding as a tool for governing the final nano-morphology, it is possible
(i) to convert even polymers inclined to form H-bonds with the water soluble part-
ner into nano-sized materials with nanofibrillar instead of network type morphol-
ogy, (ii) to use water as the only solvent, and (iii) to regenerate the water-soluble
polymer and reuse it for the same purpose.

Acknowledgments

The author would like to thank the Foundation for Research Science and Tech-
nology of New Zealand for financial support (Grant No. UOAX 0406) as well as
appreciate the hospitality of the Department of Mechanical Engineering and the
Centre for Advanced Composite Materials of The University of Auckland where
this study was completed.

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