Materials for Turbine Power Blades, Reinforcements, and Resins - Hybrid Anisotropic Materials for Wind Power Turbine Blades - page 85

η=.KM 3.4-3.5. ....above.Mc. (3.8)

The. Mc. above. which. entanglement. occurs. is. usually. thought. to. be.
on.the.order.of.5,000.to.20,000.g/mol,.depending.on.the.chemical.struc-
ture.of.the.polymer..However,.in.highly.concentrated.polymer.solutions,.
dependence.of.viscosity.on.molecular.weight.with.exponents.larger.than.
1.may.occur.at.low.molecular.weights..The.viscosity.of.vinyl.ester.resin.
increases. signiicantly. when. the. molecular. weight. of. vinyl. ester. oligo-
mers. increases. from. 690. g/mol. to. 1,000. g/mol.. For. example,. at. 35. wt.%.
styrene.concentration.at.room.temperature,.the.viscosity.of.the.cure.vinyl.
ester.resins.(VER).with.Mn.=.690.g/mol.is.521.cP,.while.that.of.the.VER.
with. Mn. =. 1,000. g/mol. is. 1050. cP.. The. high. dependency. of. viscosity. on.
the.molecular.weight.of.the.vinyl.ester.resins.of.low.molecular.weight.is.
probably. due. to. hydrogen. bonding. between. the. vinyl. ester. molecules,.
increasing.the.effect.chain.length.

3.9.6 Relations between the Viscosity, Processing,

Temperature, and Glass Transition Temperature

The.glass.transition.temperature.of.the.VER.with.Mn.=.690.g/mol.was.deter-
mined. by. differential. scanning. calorimetry. (DSC).. It. was. found. that. the.
vinyl.ester.resin.only.have.one.Tg..The.Tg.of.the.vinyl.ester.resins.decreases.
linearly.as.styrene.concentration.increases.(Figure 3.15).
For. concentrated. polymer. and. oligomer. solutions,. the. Williams-Landel-
Ferry.(WLF).equation.can.be.used.to.relate.the.viscosity.with.glass.transition.
temperature. 41 .In.general,.the.WLF.equation.holds.in.the.temperature.range.
Tg.to.(Tg.+.100 ° C):

-17.4(T - Tg)
51.6 + (T - Tg)

.

log η η Tg =

. .(3.9)

For. the. vinyl. ester/styrene. system,. a. similar. relationship. exists. between.
the.testing.temperature,.the.Tg,.and.viscosity..In.the.20.wt.%,.25.wt.%,.and.30.
wt.%.styrene.resins,.the.plots.of.logη-.(T.-.Tg). -1 (Figure 3.16).
Equation.(3.7).shows.the.line.fall.and.viscosity.of.vinyl.ester.mixtures.are.
associated. with. the. difference. between. Tg. and. the. measurement. tempera-
ture..The.curve.its.given.equation.(3.10):

253.2
T - Tg - 0 2427 .

. log η = . (3.10)