As the demand for oil and gas resources increases, the need to venture into more hostile environments becomes a dynamic focus in the petroleum industry. One problem associated with certain high risk formations is lost circulation. As a result, engineers have concentrated research efforts on developing novel Lost Circulation Materials (LCM’s) that will effectively treat thief zones. The most pioneering LCM’s require mixing energy to activate a reaction involving two or more chemicals. However, minimal research has been conducted to accurately predict downhole mixing capabilities. Therefore, this research focuses on developing a correlation between laboratory experiments and scaled model experiments for accurate prediction of downhole mixing energies in terms of flow rate for adequate mixing of lost circulation prevention fluids.

Phenol formaldehyde (PF) is the oldest known synthetic polymer. This polymer has seen many applications throughout history, including jewelry, electric wire insulation, and resins used to make adhesives. Today, PF resins are still crucial components used in the wood products industry. These PF resins are formulated into adhesives used to make plywood and various other wood composite products. For example, in the United States, 90 % of the homes are still frame homes that use plywood for construction. The PF adhesives used to make these composites are formulated using agricultural waste products like walnut shells and corn-cob residue. These organic waste products act as fillers that reduce the cost, increase the viscosity, and affect the rheology of the fillers. Wheat flour is added as an extender to reduce cost and affect the tack of the adhesive. These organic fillers are lignocellulosic materials that are made of lignin, cellulose, and hemicellulose. Not much is known about the interactions of these organic fillers and the polymer resin. Rheological studies in our lab have shown that not all of the additions to the adhesive formulation are inert components in the adhesive. The steady-state flow curve analysis of PF adhesives revealed that there is a liquid structure change that occurs at high shear rate. This structure change is observed as a viscosity increase that occurs after applying a maximum shear rate of 4000 1/s. A rheological analysis was conducted to determine the source of this change, with individual components added to the resin. The PF base resin (with nothing added) has a Newtonian rheological behavior. When wheat flour is added to the resin, the overall viscosity increases, and shear thinning occurs at highe shear rates. There is no final viscosity change observed on with the addition of wheat flour. Adding corn-cob residue to the resin increased viscosity, led to some shear thinning at higher shear rates, and allowed the viscosity changes observed in the fully formulated adhesives. These experiments showed that the liquid structural changes that occur in the adhesives are attributed to the organic fillers. All organic fillers used in our studies, including corn-cob residue, walnut shell, almond shell, and Alder bark produce different levels of viscosity change in the PF adhesive formulations. These biomass materials have varying amounts of lignocellulosic content, particle size distributions, and particle shape. Among the fillers, corn-cob residue was shown to cause the most viscosity change compared to any of the fillers. Corn-cob residue is unique compared to the others because it has undergone acid digestion to convert its xylans to furfural. During the viscoelastic oscillation studies, the corn-cob residue filled adhesives showed that they developed network structures in response to a high shear rate that were not observed using the other fillers. With the discovery of these network structures, the next goal of this research was to correlate the effects observed on the rheometer to relevant adhesive application technology like high shear spraying. The corn-cob residue adhesive was sprayed at approximately 70,000 1/s compared to the 4000 1/s of rotational shear on the rheometer. The viscoelastic oscillation studies revealed that there was no network structure formation after high-shear spraying. Further, there was no change observed in the flow curve analysis after spraying the adhesive. This study showed that there are limitations when trying to correlate changes that happen in adhesives during spraying, where extensional forces dominate compared to shear forces. In future research, there is the opportunity to explore the effects of extensional deformation that occurs during the atomization of the adhesive, which will be more reflective of the changes that occur during spraying. / Doctor of Philosophy / Phenol-formaldehyde adhesives are crucial products in the home construction industry. These adhesives are used to make plywood that is used to build frame homes, which represent approximately 90 % of the homes in the United States. These phenol-formaldehyde adhesives are made using organic materials repurposed from agricultural waste products like corn cobs, walnut shells, almond shells, and tree bark. These products help to enhance the properties of the adhesive, reduce the cost, and reduce the amount of resin used. The goal of this research is to understand better the interactions between the adhesive and the organic fillers using rheology. Rheology is a field that studies how materials change and flow with applied external forces. This is an important field because it provides information on viscosity and viscoelastic behavior. Our research has shown that in response to high shear rates, the viscosity of these phenol-formaldehyde adhesives increases. Studying these changes can lead to a better understanding of how these materials change during industrial spraying. This understanding could lead to improved building adhesive materials in the home construction industry.

<p dir="ltr">Extrusion is a complex process that is difficult to model due to the complex geometry. In addition, modeling the flow of a shear and thermal sensitive material such as waxy corn starch further complicates the problem. Starch undergoes three main transformations during processing: 1. Gelatinization, 2. Melting, and 3. Fragmentation. The first two can be combined into starch conversion and have been studied in detail, along with their effect on viscosity.</p><p dir="ltr">This work extruded waxy corn starch using the “NASA” autogenous single screw extruder with and without steam locks at moisture contents of 30% w.b. and 35% w.b. as well as screw speeds of 300 rpm and 600 rpm. A Brabender single screw was used at 100 rpm, 35% w.b., and 140°C to obtain starch at another molecular weight. Molecular weight was measured using HPSEC-MALLS-RI, and viscosity was measured using a capillary rheometer. Starch conversion was checked by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC).</p><p dir="ltr">The work extended upon previous rheological models by separating the lumped SME (specific mechanical energy) parameter into degree of starch conversion and molecular weight reduction. The new viscosity model can be combined with kinetics to predict rheology in computational fluid dynamics models that model the extrusion process. The approach can aid in designing the extrusion process and other unit operations by predicting extrusion characteristics without having to build the new design using a trial-and-error approach.</p><p dir="ltr">Additionally, a method was investigated to decouple SME into an average shear rate and mean residence time by setting SME equal to SEC (specific energy consumption). Shear history was found from the decoupled average shear rate and mean residence time. Shear history was a worse predictor for molecular weight reduction than SME alone because it was derived from SME with approximated average values from the extrusion trials.</p><p dir="ltr">Finally, the effect of steam locks in the “NASA” extruder was investigated and found to marginally reduce molecular weight, reduce the mass flow rate and increase the mean residence time for every condition except at a screw speed of 600 rpm and moisture content of 30% w.b. The work as a whole demonstrates the importance of understanding how materials change during processing.</p>