production of selected secondary metabolites in transformed ...

Then, the solubility parameter can be estimated from general equations:
ΔHmix = Vs(δ1 – δ2) * φ1 φ2 .
- This is one of the simple expressions of solubility parameter deduced for nonpolar
systems. In practise, we have solvents and solutions with different polar forces such as
dispersion, polar and hydrogen ones. Therefore the cohesive energy Ecoh is divided into three
parts, corresponding to three types of interaction forces Ecoh = Ed + Ep + Eh (contribution of
dispersion forces Ed, polar forces Ep and hydrogen-bonding Eh). Then every substance could
be characterized according to free contributions of total solubility parameter
2 2 2
δtotal.= σ + σ + σ .
disp.
polar.
hydrogen.
By this is predicted that if δ1 = δ2 the ethalpy of mixing is ΔHmix = 0 and ΔGmix = ΔHmix -
TΔSmix < 0 and this is in accorrdance with the general rule for thermodynamic view of
solubility and mixing. Then, the smaller is the difference of value δ of solvent and polymer,
the better is possibility of its dissolving. The polymers should be mostly soluble in that
solvents, which their < δ > correspond to the middle of the interval of polymer solubility or
approximately ± 2 units.
AIM OF STUDY:
The aim of conducted research is the evaluation of influence of several aspects – especially
structure of samples – on the chemical resistance of PUR coatings and the value of their
solubility parametr δ2. As far as these aspects are concerned, these include especially the type
of used monomers (in case of PUR polymers for example like type and funcionality of used
alcohols, acids and isocyanates, type of bonds, etc.), the weight, size and type of film forming
polymer and the type of interactions between individual chain parts.
METHOLOGY:
The solubility parameter δ2 of polymer could be determined according to its interaction
with solvents of known solubility parameter δ1. For example, the solubility parameter of a
linear polymer can be determined from its limiting viscosity number and of a cross-linked
one according to the degree of swelling, both of these values being the function of solubility
parameter of used solvent δ1. In case of best solvent, is the value of [η] or Q of polymer the
heights and solubility parameter of this solvent δ1 correspondents with solubility parameter of
polymer δ2
As far as measuring of viscosity is concenred, the samples were dissolved in selected
group of solvents whose solubility parameters δ1 varied from 18 to 24 (30). Then their
dynamic viscosity η were masured. It was done using capillar or Ubelohde viscosimeter.
η sp
Subsequently, specific viscosity ηspec and the limiting viscosity number [η] = lim were
c→0
c
calculated.
The degree of sample’s swelling Q = (m-m0/m0)*1/ςsolv was calculated by weighting
samples after soaking in chosen solvents for 5 days.
Sborník soutěže Studentské tvůrčí činnosti Student 2006 a doktorské soutěže O cenu děkana 2005 a 2006
Sekce DSP 2006, strana 250