Date of Award

May 2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

First Advisor

Yun Ji

Second Advisor

Peter W. Hart

Abstract

Additives are ingredients used in papermaking to enhance fiber properties, introduce special properties to the paper and improve the efficiency of the paper making process. Wet strength agents, sizing agents, dry strength agents, fillers, retention aids, defoamers, dyes and pigments are common additives used in paper mills. Poor retention of wet strength additive such as PAAE (polyamide epichlorohydrin) and hydrophobicity loss due to ASA (alkenyl succinic anhydride) and AKD (alkyl ketene dimer) size reversion not only increase cost and reduce product quality in the mill but also increase customer complaints and rejections.In this study, a method was developed to quantify and study the parameters that govern PAAE retention in paperboard. PAAE applications, performance, and recyclability were also investigated. In addition, ASA bonding mechanism to the fiber was investigated, and experiments were performed under different environmental conditions to determine the environmental parameters that initiate or catalyze ASA and AKD size reversion. The results of these studies indicated that PAAE can be quantified after hydrolysis and derivatization to diethyl adipate. PAAE retention increases as the pulp freeness decreases. Instead of freeness, fiber surface charge can be used to predict PAAE retention. The results also indicated that high presence of lignin in the sheet provides wet strength and low PAAE retention due to low availability of carboxylic groups on the fiber. On the contrary, when the lignin is removed, the retained amount of cationic PAAE increases due to the availability of anionic carboxylic groups on the fiber resulting in high wet strength; lignin is potential biomaterial based wet strength. Investigations revealed that ester bond formation between ASA and cellulose is insignificant and is not a prerequisite for sizing effectiveness. Although, hydrolyzed ASA contributes to the sizing performance, direct application of hydrolyzed ASA to the pulp leads to flocculation and does not achieve sizing. The results revealed that ASA and AKD size reversions are significantly light and oxygen dependent. The oxidative photodegradation mechanisms of the sizing agents are explored and possible mechanisms are proposed.

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