Revealing Adsorption Behaviors of Amphoteric Polyacrylamide on Cellulose Fibers and Impact on Dry Strength of Fiber Networks

Abstract

Amphoteric polyacrylamide (AmPAM) has been widely used in a variety of industrial areas and the adsorption behavior of AmPAM plays a crucial role in its applications. In this study, a series of AmPAMs with various molecular weights (MW) were synthesized; and their impact on dry strength of fiber networks or paper was assessed. The results showed that the optimal MW of AmPAM for strength enhancement ranged between 300 and 500 k. More importantly, the adsorption behaviors of three typical AmPAM samples on silica (model substrate) and cellulose surfaces were revealed using a quartz crystal microbalance with dissipation monitoring (QCM-D) in situ and in real time. The adsorption dynamics of AmPAM and the conformation of the adlayers were further derived. The results indicated that a relatively high adsorption amount was achieved under the conditions of a high polymer concentration, a medium pH close to its isoelectric point (IEP), a mild ionic strength, and a high charged surface; whereas the MW of AmPAM had little effect on the equilibrium adsorption mass of AmPAM, but significantly affected the conformation of adsorbed layer on substrates. Based on the adsorption behaviors of AmPAM, the explanation of the best dry strength achieved in a narrow range of MW of AmPAM is proposed. It was concluded that the appropriate balance between bridging and flocculation, penetration into fiber pores, and conformation were only achieved in the optimal MW range of AmPAM. The findings obtained from in this work enable us to better understand the adsorption behaviors of polyampholyte, and provide a guideline on molecular design of AmPAM and its applications from both fundamental and practical points of view.

Surprising Nanomechanical and Conformational Transition of Neutral Polyacrylamide in Monovalent Saline Solutions

“…Notice that the curves overlapped well in the high force region, indicating that they correspond to the elongation of single-molecule NPAM. 61,62 At low force region (<1000 pN), F−E curves obtained in 0.5 M KAc and in DI water are higher than that obtained in DMSO, while the curve obtained in KSCN shows the opposite trend. Ulteriorly, the stretching energy (defined ΔE) of NPAM in aqueous conditions comparing to that in DMSO (represent the backbone elasticity) were obtained by calculating the area difference between the curves, which can be used to describe the nanomechanical properties of NPAM.…”

Quartz crystal microbalance with dissipation (QCM-D) as a way to study adsorption and adsorbed layer characteristics of hemicelluloses and other macromolecules on thin cellulose films: A Review

“…Adsorption of PEDOT:PSS was found to be a spontaneous reaction driven by entropy gain. Zhang et al (2019) studied the adsorption behavior of amphoteric polyacrylamide (AmPAM) as a papermaking additive on microcrystalline cellulose (MCC) and use QCM-D to monitor the effect of different molecular weights of AmPAM on adsorption in real time. It was concluded that the optimal molecular weight range for increasing the dry strength of paper was between 300k and 500 k.…”