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NOVEL ON-LINE TRUE STRESS-STRAIN-ELECTRICAL CONDUCTIVITYUNIAXIAL TENSILE STRETCHING SYSTEM AND ITS UTILITY ON ELECTRICALLYCONDUCTIVE POLYLACTIC ACID (PLA) NANOCOMPOSITES

Kwa, Teik Lim
http://rave.ohiolink.edu/etdc/view?acc_num=akron1143663747

Abstract Details

2006, Master of Science in Polymer Engineering, University of Akron, Polymer Engineering.
The main goal of this research is to develop anintegrated uniaxial stretching system that allows simultaneousmeasurement of electrical conductivity, true stress and true strainduring free-width uniaxial deformation of electrically conductivepolymers. Percolation curve for biodegradable Poly lactic acidfilled with high structure carbon black was constructed and thepercolation curve was found to be precipitously increased andsensitive at the critical percolation concentration (5 wt% forbinary system). In order to reduce this, organically modifiednanoclay was introduced at small concentrations and this was foundto partially block the electron conducting pathways thereby causingthe reduction of the sensitivity of the percolation curve. This,then allows for development of conductive compositions to beobtained at intermediate conductivity levels (10-5 - 10-10 S/cm)that are needed for electrostatic discharge applications includingelectronic packaging. Using the newly developed real timemeasurement system, we have investigated the temperature dependencyof electrical conductivities of selected binary nanocomposites.Positive temperature coefficient (PTC) behavior (decrease ofconductivity with increase of temperature) was observed from roomtemperature to Tg+20. This is attributed to increase of gapseparation in the conductive pathways established by the carbonblack due to much higher thermal expansion coefficient of the PLAmatrix as compared to those of the fillers. Above this temperaturerange the originally amorphous matrix begins to crystallize andthis resulted in increase of electrical conductivity. The expulsionof dispersed CB particles by the growing crystallites to theirboundaries leading to formation of added branches in the conductivenetwork could cause such an increase during the coldcrystallization process. Heating beyond this range resulted inaccelerated increase in conductivity when the matrix melts. Sinceall parameters are continuously monitored before, during and afterthe stretching, the newly developed instrumented stretching systemallowed us to track them during heating, uniaxial stretching,holding and cooling. This allowed a complete laboratory simulationof a typical thermo-deformation cycle of a film undergoes duringthe course of a commercial film stretching process. The resultsindicated that electrical conductivity at the rubbery temperaturerange (Tg<T<Tcc) exhibited moderate increase duringstretching for both PLA/CB and PLA/CB/Nanoclay systems. This mainlyoccurs due to machine direction orientation of the conductive CBnetwork as revealed by TEM. However, during holding stage,conductivity of binary system exhibited slight decrease whererelaxation of PLA molecular chains drifted away certain amount ofCB network and caused the development of larger inter-particlesgap. Contrary to binary system, during holding stage the ternaryPLA/CB/Nanoclay nanocomposite exhibited subsequent increase inelectrical conductivity implying the enhancement of organization ofCB network aided by the clay particles that were found to orientwith normals of their surfaces in the transverse direction.Conductivity remains at the final state when both binary andternary systems are cooled to room temperature. We also observedthat high speed stretching induced preferential machine directionalignment of CB networks. However, increasing fraction ofinterparticle gaps leads to slower increase in conductivity athigher stretching rates as revealed by TEM observations.
Mukerrem Cakmak (Advisor)
PLA nanocomposites; electrical conductive; PTC; true stress-true strain-electrical conductivity; preferential alignment of CB networks

Recommended Citations

Citations

  • Kwa, T. L. (2006). NOVEL ON-LINE TRUE STRESS-STRAIN-ELECTRICAL CONDUCTIVITYUNIAXIAL TENSILE STRETCHING SYSTEM AND ITS UTILITY ON ELECTRICALLYCONDUCTIVE POLYLACTIC ACID (PLA) NANOCOMPOSITES [Master's thesis, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1143663747

    APA Style (7th edition)

  • Kwa, Teik Lim. NOVEL ON-LINE TRUE STRESS-STRAIN-ELECTRICAL CONDUCTIVITYUNIAXIAL TENSILE STRETCHING SYSTEM AND ITS UTILITY ON ELECTRICALLYCONDUCTIVE POLYLACTIC ACID (PLA) NANOCOMPOSITES. 2006. University of Akron, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1143663747.

    MLA Style (8th edition)

  • Kwa, Teik Lim. "NOVEL ON-LINE TRUE STRESS-STRAIN-ELECTRICAL CONDUCTIVITYUNIAXIAL TENSILE STRETCHING SYSTEM AND ITS UTILITY ON ELECTRICALLYCONDUCTIVE POLYLACTIC ACID (PLA) NANOCOMPOSITES." Master's thesis, University of Akron, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=akron1143663747

    Chicago Manual of Style (17th edition)

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This open access ETD is published by University of Akron and OhioLINK.