|1.||Gradys A., Geometrical effects during crystallization under confinement in electrospun core-shell fibers. DSC study of crystallization kinetics, POLYMER, ISSN: 0032-3861, DOI: 10.1016/j.polymer.2016.12.009, Vol.108, pp.383-394, 2017|Gradys A.
, Geometrical effects during crystallization under confinement in electrospun core-shell fibers. DSC study of crystallization kinetics
, ISSN: 0032-3861
, DOI: 10.1016/j.polymer.2016.12.009
, Vol.108, pp.383-394, 2017
Calorimetric studies on poly(ethylene glycol) Mn = 400 g/mol, encapsulated in polystyrene fibers show non-trivial crystallization behavior. Analysis, assuming constant Avrami exponent n, is unsuitable. Approach allowing for changes in the exponent n, requires assumption of the crystallization rate function, derived from the nucleation theory. Changes in Avrami exponent n, follow the changes in geometry of crystal growth and in nucleation mechanisms. Crystallization in micrometer fibers starts from heterogeneous nucleation with three-dimensional crystal growth e as in bulk e but changes to two and one-dimensional, terminated by homogeneous nucleation. For bulk and in 1 and 0.6 micron thick fibers, the approach evidences similar thermodynamic parameters. In 0.6 micron thick fibers, crystallization rate is lower due to higher energy barrier for diffusion, ED = 10 kJ/mol versus 8.7 kJ/mol for bulk and 1 micron thick fibers. Additionally, fiber thickness depends not only on parameters of the electrospinning process but also on the thermal history.
Core-shell fibers, Confinement effects, Crystallization kinetics, DSC, Polyethylene glycol
|2.||Urbanek O., Sajkiewicz P., Pierini F., Czerkies M., Kołbuk D., Structure and properties of polycaprolactone/chitosan nonwovens tailored by solvent systems, Biomedical Materials, ISSN: 1748-6041, DOI: 10.1088/1748-605X/aa5647, Vol.12, No.1, pp.015020-1-12, 2017|Urbanek O.
, Sajkiewicz P.
, Pierini F.
, Czerkies M.
, Kołbuk D.
, Structure and properties of polycaprolactone/chitosan nonwovens tailored by solvent systems
, Biomedical Materials
, ISSN: 1748-6041
, DOI: 10.1088/1748-605X/aa5647
, Vol.12, No.1, pp.015020-1-12, 2017
Electrospinning of chitosan blends is a reasonable idea to prepare fibre mats for biomedical applications. Synthetic and natural components provide, for example, appropriate mechanical strength and biocompatibility, respectively. However, solvent characteristics and the polyelectrolyte nature of chitosan influence the spinnability of these blends. In order to compare the effect of solvent on polycaprolactone/chitosan fibres, two types of the most commonly used solvent systems were chosen, namely 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and acetic acid (AA)/formic acid (FA). Results obtained by various experimental methods clearly indicated the effect of the solvent system on the structure and properties of electrospun polycaprolactone/chitosan fibres. Viscosity measurements confirmed different polymer–solvent interactions. Various molecular interactions resulting in different macromolecular conformations of chitosan influenced its spinnability and properties. HFIP enabled fibres to be obtained whose average diameter was less than 250 nm while maintaining the brittle and hydrophilic character of the nonwoven, typical for the chitosan component. Spectroscopy studies revealed the formation of chitosan salts in the case of the AA/FA solvent system. Chitosan salts visibly influenced the structure and properties of the prepared fibre mats. The use of AA/FA caused a reduction of Young's modulus and wettability of the proposed blends. It was confirmed that wettability, mechanical properties and the antibacterial effect of polycaprolactone/chitosan fibres may be tailored by selecting an appropriate solvent system. The MTT cell proliferation assay revealed an increase of cytotoxicity to mouse fibroblasts in the case of 25% w/w of chitosan in electrospun nonwovens.
chitosan, electrospinning, PCL/chitosan fibres, solvent system, chitosan salts