Barbieri Thesis - BioMedical Materials program (BMM)

Chapter 4 – Conntrol
of mechanical
and degraddation
properties s in composites
the polymmer
in M50 haas
significantly y lower viscosiity
than M25 and a M0. In general
it is
expected that polymerss
with shorter and looser chhains,
i.e. having
lower visc cosity, are
more flexxible
and thus more prone to o dissipate ennergy
during th he stress. The erefore, in
spite of itts
higher stiffnness,
M50 had d larger dampping
properties s by virtue of the lower
viscosity of its polymer phase.
Increasing
amounts off
apatite partic cles increasedd
the hydrop philicity (Figur re 4) and
the capaacity
of commposites
to uptake u fluids (Table 4). This fact ha ad large
implications
on the mechanical properties since, in presence
of water, w the
stiffness oof
the materiaals
containing apatite, i.e. MM25
and M50, largely decreased.
On
the contrary,
the mostt
hydrophobic material (i.e. . M0) kept its initial stiffnes ss. Water
may havee
seeped morre
into the ma aterials with hhigher
apatite content, rend dering the
apatite/poolymer
contaacts
less sta able and addding
more freedom f in molecular m
movemennts
decreasingg
in this way the storage modulus. Thu us, besides having
the
lowest viscosity
polymmer
phase, M50 also abbsorbed
more e water and thus its
mechaniccal
stiffness ddecreased
mo ost. Water also
had a plasticizer
effect rendering
the polymmer
phase moore
viscoelastic,
as shown bby
an increas se of the tange ent for all
materials (Figure 6d) . Interestingly y, the increaasing
damping g properties occurred
largely foor
materials wwith
increasin ng apatite conntents
since, besides havi ing lower
polymer vviscosity,
theyy
had larger ab bility to uptakee
water.
Figure 6. SStorage
modulus of the materials in i (a) dry and (c) ) wet conditions. Loss tangent in ( b) absence
and (d) pressence
of water.
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