Date of Award

Spring 5-5-2023

Level of Access Assigned by Author

Open-Access Thesis

Language

English

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

Advisor

Douglas W. Bousfield

Second Committee Member

William J. DeSisto

Third Committee Member

Albert Co

Additional Committee Members

Mehdi Tajvidi

John Roper

Abstract

The dynamic penetration of fluid into a porous media where other changes are occurring such as temperature or concentration is of interest to a number of situations. However, little experimental and theoretical analysis of this situation is found in the literature where most of the previously published works have studied the penetration with constant physical properties, where there is no change of the fluid as it enters the pores. This situation is important in the setting of adhesives in porous medium such as in the setting of hot melt and water-based adhesives in the production of paper based packaging. The controlled penetration of the adhesive is important to obtain rapid setting rates and good bond strength. However, the degree of penetration depth of adhesives into systems like paper was limited to cross-sectional images and no quantitative method is well established in the literature. The analysis of these images is difficult especially if there is an interaction between the adhesive and the pores inside the porous mediums. In addition, little has been published on the rate of adhesive setting and final bond strength as a function of fundamental parameters such as pore size distribution, adhesive properties, and process parameters such as pressure and temperature.

Experiments were designed to understand the extent of penetration of hot melt and water-based adhesives into several porous coated and uncoated papers. Methods to characterize penetration depth were developed and compared: one method, based on silicone oil absorption, was found to be accurate and convenient. Tests were performed to determine the penetration depth as a function of the characteristics of the paper such as the pore size distribution, porosity, permeability, and other parameters such as paper temperature, adhesive temperature or concentration, contact pressure and time. Paper surfaces were modified by a range of coatings that have different porosities and pore sizes, and contact angles; these surfaces were characterized with a range of techniques.

The results of the setting of hot melt adhesive show that more penetration when the paper is hot and less penetration when the latex level increases in the coating layer due to the reduced permeability. For the range of pigments used in this study, the influence of the pigment size particle on the penetration depth was minor. Mechanical testing confirmed that more penetration leads to stronger bond strength. The water-based adhesive on the other hand, at various solids contents, was applied to the paper surfaces in a press as well varying press pressures and times. Similar to the setting of the hot melt adhesive, the results showed more penetration when the paper is uncoated and less penetration when the latex level increased in the coating layer. The significant finding here is that the different press pressures and times and solids contents of adhesive did not significantly change the degree of penetration depth for the same type of paper used. Various other tests indicate that this result is due to the adhesive that is able to clog pores and stop flowing. This clogging mechanism can be related to the dewatering of the adhesive inside the pore space in which the adhesive increases in viscosity as water leaves into the paper fibers. This finding was supported by the mechanical Instron testing that showed similar loads for the samples that have the same penetration depths except for the sample that has a higher latex level which is due to the strong coating layer that needs higher force to peel. Reducing the adhesive amount and changing the paper type were other examples that confirmed these two mechanisms. The green bond strength was also obtained for all samples using the roll press test. The green bond strength was low compared to the final bond strength of the same sample.

Various models were developed to predict the penetration of the adhesive as a function of the fundamental parameters. A model based on the unsteady-state flow of a polymer into a pore that includes dynamic heat or mass transfer is developed using a finite element method-based model (COMSOL Multiphysics 5.5) and compared to a modified Lucas-Washburn equation where the viscosity was a function of temperature (hot melt adhesive) or concentration (water-based adhesive). In addition, a model was developed based on Darcy’s law to describe the penetration accounting for changes in fluid properties and account for different layers of pore space and the limited supply of adhesive. These models consider the change of viscosity of the fluid as it enters the pore structure. These models were compared to the experimental results and some simple experiments. Good agreement within a reasonable range for different papers, pressing times and pressures, paper temperatures, and adhesive solids contents is obtained. For the dynamic heat transfer model, a new dimensionless group called D* is proposed that can help predict if cooling in the pore is important or not: if D* > 1000, cooling is not expected to occur and large penetration happens. For the dynamic mass transfer model on the other hand, another dimensionless group called Z* is proposed to determine if solvent diffusion is important or not. When this group is large, over 5×106, diffusion is minimal and large penetration happens.

The net outcome of this research is to provide a better understanding of the dynamic behavior during the process of penetration of adhesives into various porous surfaces as well as in specifying the key parameters that mostly affect the rate of setting, the depth of penetration, and the strength of green and final bond in a flow that involves temperature and concentration changes. To our knowledge, this is the first attempt at trying to predict the dynamic penetration of an adhesive into a porous structure in this manner where it will advance the knowledge and help the industry overcome this type of problem. In addition, this should be the first time where the model is compared directly to experiments where most of the parameters are well-known.

Download

Share