Browsing by Author "Dr. Orlando J. Rojas, Committee Member"

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Analysis of Properties of Synthetic Mineral Microparticles for Retention and Drainage System.
(2007-03-08) Lee, Sa Yong; Dr. Lucian A. Lucia, Committee Member; Dr. Joel J. Pawlak, Committee Member; Dr. Orlando J. Rojas, Committee Member; Dr. Martin A. Hubbe, Committee Chair
Over the past 20 years, nano- or macro-sized particles have been used revolutionary as a component of drainage and retention systems for paper making. More recently a group of patented technologies called Synthetic Mineral Microparticles (SMM) has been invented. This system has potential to further promote the drainage of water and retention of fine particles than bentonite during papermaking as shown in the prior research. In spite of the demonstrated advantages of this SMM system, the properties of SMM particles in the aqueous state haven't been elucidated yet. Streaming current and potentiometric titration were employed to characterize the charge behavior of SMM, depending on the synthetic conditions, including variation of the Al⁄Si ratio, partial neutralization of aluminum, salt addition and shear rate. Surface area of SMM and the distribution of SMM particle size were investigated with scanning electron microscopy in order to elucidate the relationship between the morphology and coagulation behavior of SMM, versus the pre-stated synthetic conditions, as well as to estimate the optimal conditions to produce SMM as a retention and drainage aid for papermaking. Streaming current titration experiments showed that pH variation, caused by the change of Al⁄Si ratio and partial neutralization, profoundly affects the charge properties of SMM, on account of the variation of Al-ion speciation and the ionizable groups on the Si-containing particle surfaces. The relationship between Al/Si ratio and isoelectric pH, measured by potentiometric titration, was estimated through statistical estimation, using a factor, the OH⁄Al ratio. This procedure permits estimation of the Al/Si ratio values at which the SMM particles are expected to have negative net charges, as required for promotion of retention and dewatering during papermaking. The structural characteristics of SMM particles could be explained in terms of the effects of ionic charges on colloidal stability of primary particles during formation of the SMM.
On the Propensity of Lignin to Associate; Static Light Scattering Measurements
(2008-06-02) Contreras Sulbaran, Irma Sofia; Dr. Orlando J. Rojas, Committee Member; Dr. Dimitris S. Argyropoulos, Committee Co-Chair; Dr. Lucian A. Lucia, Committee Chair
Performance Evaluation of Chemical Protective Clothing Materials under Dynamic Mechanical Deformation
(2005-07-13) Shiels, Brian Patrick; Dr. Juan P. Hinestroza, Committee Chair; Dr. Roger L. Barker, Committee Co-Chair; Dr. Morteza G. Khaledi, Committee Member; Dr. Orlando J. Rojas, Committee Member
This thesis presents a comprehensive assessment of testing methodologies currently used for evaluating the performance of protective clothing materials. Special emphasis is placed on highlighting the inadequacy of such test methods and their lack of correlation with real life scenarios which may introduce mechanical deformation. ASTM F23 standardized rubber sheets were used to evaluate the sorption, permeation and penetration behavior of the samples when exposed to a standardized liquid challenging agent. 2-Chloro-1,3-butadiene (neoprene) was used as the standard chemical protective clothing material and liquid acetone was selected as the standard challenging agent. The dynamic mechanical properties of the samples were assessed via creep and stress relaxation testing techniques using customized submersion clamps. Quantitative agreement between sorption and permeation experimental data validated the concept that diffusion was the rate-limiting step for the transport of acetone through neoprene rubber. Creep and stress relaxation experiments illustrated a strong time dependency of the storage and loss modulus of the neoprene samples when exposed to the challenging agent. The Young's modulus of the standard material was also found to be a decreasing function of the number of loading-unloading cycles highlighting the effect of mechanical deformation of the barrier properties of protective clothing materials. Potential improvements to existing testing methodologies are proposed and discussed in detail.