Swelling Behavior

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    Sorption PropertiesEnhancement of

    Composites: HygroscopicThickness Swelling

    Aileen Grace M. OngkikoMS Materials Science & EngineeringDepartment of Mining, Metallurgical &Materials EngineeringCollege of EngineeringUP Diliman

    28 March 2011

    National Engineering CenterUP Diliman

    MSE 282

    Composite

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    Wood fiber/polymer composites

    Wood fiber/polymer composite ismanufactured by dispersing woodparticles into molten plastic with

    coupling agent or additives to form

    composite material through varioustechniques of processing such asextrusion, compression or injection

    moulding.Better dimensional stability and

    durability against bio-deterioration as compared to

    wood.

    As compared to polymers, highermechanical properties, thermalstability and more resistance to

    ultraviolet light and degradation.

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    Thickness Swelling Stages of WoodComposites

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    Shi and Gardner(2005)

    Relative swelling rate DECLINESlinearly;

    INCREASE in board thickness

    T

    T

    Thickness swelling (TS) = f(specimen

    thickness)

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    Fabrication of Wood fiber/polymer composite& Hygroscopic Thickness Swelling TestShi and Gardner (2005)

    Thermomechanical fibers pulping (TMP): 75% aspen & 25% otherhardwoodsPolymer fluff: polyurethane, polypropylene, poly(vinyl chloride),acrylonitrile, butadiene/styrene (ABS); processed from reclaimedautomobile polymer mixturespMDI Polymeric diphenylmethane diisocyanate

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    Effect of ambient environment on thehygroscopic thickness swelling rateShi and Gardner (2005)

    1. The swelling model fits the experimental dataquite well for most of the cases.

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    Effect of ambient environment on thehygroscopic thickness swelling rateShi and Gardner (2005)

    2. The thickness swelling of wood fiber/polymercomposites was about 30% lower than that of thewood fiberboard.

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    Effect of ambient environment on thehygroscopic thickness swelling rateShi and Gardner (2005)

    3. The higher the temperature, the greater theswelling rates of the composites.

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    KSR

    Temperature (C)

    Relationship of temperature and swelling rate of the wood fiberboard and wood

    fiber/polymer composites.

    Woodfiberboard

    Woodfiber/PolymerComposite

    Activation energyWood fiberboard: 14.91KJ/moleWood fiber/polymer composite:

    13.33 KJ/mole

    Temperature have less effect on theswelling rate for wood fiber/polymer

    composites than that for neat woodfiberboard.

    ff f bi i h

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    Effect of ambient environment on thehygroscopic thickness swelling rateShi and Gardner (2005)

    4. RH has a significant effect on the hygroscopicthickness swelling process of the woodfiber/polymer composites.

    EMC RH

    Actual RHs in the experimentalenvironment can possibly deviate

    from the target RHs;

    EMC was used to describe how RHaffects the TS or the swelling rate

    Linear relationship between TS and EMC

    Eff f bi i h

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    Effect of ambient environment on thehygroscopic thickness swelling rateShi and Gardner (2005)

    5. Hygroscopic thickness swelling rate has a poorrelationship with RH for both samples.

    RH; greater concentration gradientfor the moisture diffusion in the

    materialRH; Thickness swelling rate

    RH; water vaporSpecimens may be equilibrated in

    moisture quicker & less time isneeded for the specimen to attain the

    equilibrium thickness.

    As the RH INCREASES, the swellingrate DECREASES

    Eff t f bi t i t th

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    Effect of ambient environment on thehygroscopic thickness swelling rateShi and Gardner (2005)

    6. Higher RH and lower swelling rate the better theprediction obtained from the swelling model.

    Higher RH, more water molecules arepresent in the environment & the

    more hygroscopic aspect contributedto the hygroscopic thickness swelling

    process

    The specimens with a higherswelling rate would have more

    potential to have more innerdebonding or damage changingthe mode of moisture uptake.

    Change in pure diffusion

    controlled swelling to a swellingincluding fracture inside the

    specimen which may induce moreerror in the swelling model

    prediction.

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    Characteristics of Shi and Gardner Model

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    ReferenceShi, S.Q. and D.J. Gardner. 2006. Hygroscopic

    thickness swelling rate of compression moldedfiberboard and wood fiber/polymer composites.Composites: Part A, 37, pp. 1276-1285.