Excited States Assignment for Ti-Doped MgAl2O4 Spinel Crystals

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Nov 15, 2013 (3 years and 10 months ago)

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INFLUENCE OF COMPOSI
TION AND THERMAL TRE
ATMENT ON THE
MOLECULAR DYNAMICS

OF PEO/PLLA
BLENDS

A.R.
Brás
(
1
)
,
P.
Malik (2),
C. Rodrigues (1),
J. Mano (2)
,
M.

Dionísio

(1)

(1)

REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia
,

Universid
ade Nova de Lisboa, 2829
-
516
Caparica, Portugal

(
2
)

3B’s Research Group


Biomaterials, Biodegradables and
Biomimetics, Campus de Gualtar, 4710
-
057, Braga, Portugal

madalena.dionisio
@dq.fct.unl.pt



Poly(L
-
lactic acid) (PLLA) and
P
oly(ethylene oxide) (PEO)

blends
with 95/5, 90/10, 85/15 and 70/30 composition in weight,
have been studied by Differential Scanning Calorimetry
(DSC)
and Dielectric
Relaxation
Spectroscopy

(DRS)
.

All blends were found to have semi
-
crystalline PLLA by compari
ng

the heat of crystal
lization and the heat of fusion of the
PLLA fraction

as quantified by DSC.

Moreover, the relaxation process
detected by DRS,
associated to the
PLLA
dynamic
glass transition
in the blends
,

shifts to
lower

frequencies/
higher

temperatures

as compared with the

completely amorphous
PLLA.

I
n
blends
containing less than 15% weight
as the PEO weight % increases the glass transition
detected
increases.
On the other
hand the melting endotherm is almost unchanged

for PLLA fraction. Concerning

PEO fraction

no melting e
ndotherm could
be detected
, by DSC and a relaxation process most likely related to the

-
relaxation of PEO was observed by DRS.
More
,
under cooling this process becames extinguished due to
n
on
-
isothermal crystallization
.

In blends with
30

weight % PEO no a
ccurate PLLA crystallization temperatures could be determined because of overlap of
the PEO melting peak and th
e PLLA crystallization exotherm; a
lso, no clear glass transition could be distinguished.

Only the
melting of both PEO and PLLA fraction emerged c
lear.


Acknowledgement
: Financial support to Fundação para a Ciência e Tecnologia (FCT, Portugal
)

through the project
PTDC/CTM/64288/2006 and
POCTI/FIS/61621/2004

is acknowledged. A. R. Brás acknowledges FCT for a PhD grant
SFRH/BD/23829/2005.