Materials for Turbine Power Blades, Reinforcements, and Resins - Hybrid Anisotropic Materials for Wind Power Turbine Blades - page 82

Rheological.behavior.of.resins.has.inluenced.hybrid.composites..This.behav-
ior.involves.different.phenomena,.such.as.viscosity.low,.rubber-like.elastic-
ity,.viscoelasticity..Such.a.study.is.important.because.viscosity.is.traditionally.
regarded.as.a.most.important.characteristic.of.resin.behavior.

3.9.2 Viscosity

Viscosity. is. the. measurement. of. a. luid's. resistance. to. low. 3 . For. a. liquid.
under. shear,. the. rate. of. deformation,. or. shear. rate,. is. proportional. to. the.
shearing.stress..Newton's.law.states.that.the.ratio.of.the.stress.to.the.shear.
rate. is. constant.. That. constant. is. viscosity.. The. common. units. of. viscosity.
are.poise.(P),.grams.per.centimeter.second.(g/cent.sec),.or.dyne.second.per.
square.centimeter.(dyn.s/cm 2 )..The.centipoise.(cP).one.hundred.poise.is.the.
most.common.unit.
The.SI.unit.of.viscosity.is.Pascal.seconds.(Pa.s.and.mPa.s.(1.mPa.s.=.1.cP)). 5,36
Viscosity.is.an.important.parameter.for.the.online.injection.molding.pro-
cess.. Epoxy. and. vinyl. ester. resins. need. to. have. a. low. viscosity. in. order. to.
low.into.the.ibers.and.to.permit.good.wetting.of.the.carbon.ibers..Styrene.
was.used.as.a.diluent.to.decrease.the.viscosity.of.the.vinyl.ester.resins.
Thus,.the.styrene.concentration.is.an.important.factor.to.control.the.vis-
cosity.of.resins..Viscosity.is.highly.sensitive.to.changes.in.temperature,.and.
the. molecular. weight. of. the. oligomers. also. affects. viscosity.. The. effect. of.
temperature.and.the.effect.of.sterene.on.viscosity.has.been.investigated. 7,8,37

3.9.3 Effect of Styrene Contents

The. viscosity. of. the. initial. resins. must. be. low. in. order. to. provide. eficient.
low. of. the. resin. into. the. iber. preforms. in. an. online. molding. process.. A.
Brookield.digital.viscometer.was.used.to.measure.the.viscosities.of.molding.
resins,.such.as.epoxy.or.vinyl.ester..The.zero.shear.viscosity.was.determined.
by. direct. extrapolation. of. low-shear. data. from. the. plot. of. viscosity. versus.
shear. rate.. The. viscosities. were. measured. for. a. series. of. resins. (vinyl. ester.
molecular. weight. =. 690. g/mol). with. increasing. styrene. concentrations. at.
room.temperature.(Figure 3.13).]
The.viscosity.of.vinyl.ester.decreases.with.increases.in.styrene.concentra-
tion.and.can.be.calculated.using.the.equation.(3.4):

. logη=.7.45.-.0.187(%St).+.0.00143(%St) 2 . (3.4)

Vinyl. ester. resins. with. varying. styrene. concentrations. provide. a. system.
with. a. wide. range. of. viscosities,. which. are. suitable. for. infusion. molding.
processes..These.resins,.with.higher.styrene.concentrations,.offer.improved.
resistance.to.acids.and.alkalis,.while.those.with.lower.styrene.concentrations.
afford.better.resistance.to.solvent. 37