Sizing performance of alkenyl succinic anhydride (ASA) emulsion stabilized by polyvinylamine macromolecules

Alkenyl Succinic Anhydride: The Question of Covalent Bonding and Chemistry Considerations for Better Sizing-Review

Alkenyl Succinic Anhydride (ASA) is a sizing agent used in papermaking to increase the water repellency of paper. Almost 60 years after the introduction of the chemical in papermaking, scientists still have differing views on how ASA interacts with cellulose. Several experiments were conducted to bring more clarity to the ASA sizing mechanism, especially on the contentious question of ASA-cellulose covalent bonding or the esterification reaction between ASA and cellulose during papermaking. Herein, research papers and patents, including experiments and results, from the 1960s to 2020 were reviewed. Our investigation revealed that the ester bond formation between ASA and cellulose is insignificant and is not a prerequisite for sizing effectiveness; the main ASA-related material found in sized paper is hydrolyzed ASA or both hydrolyzed ASA and ASA salt. In addition, ASA emulsion stability and ASA emulsion retention are important for sizing efficiency improvement.

Chemical Gradients in Polymer-Modified Paper Sheets-Towards Single-Layer Biomimetic Soft Robots

Biomimetic actuators are typically constructed as functional bi- or multilayers, where actuating and resistance layers together dictate bending responses upon triggering by environmental stimuli. Inspired by motile plant structures, like the stems of the false rose of Jericho (Selaginella lepidophylla), we introduce polymer-modified paper sheets that can act as soft robotic single-layer actuators capable of hygro-responsive bending reactions. A tailored gradient modification of the paper sheet along its thickness entails increased dry and wet tensile strength and allows at the same time for hygro-responsiveness. For the fabrication of such single-layer paper devices, the adsorption behavior of a cross-linkable polymer to cellulose fiber networks was first evaluated. By using different concentrations and drying procedures fine-tuned polymer gradients throughout the thickness can be achieved. Due to the covalent cross-linking of polymer with fibers, these paper samples possess significantly increased dry and wet tensile strength properties. We furthermore investigated these gradient papers with respect to a mechanical deflection during humidity cycling. The highest humidity sensitivity is achieved using eucalyptus paper with a grammage of 150 g m^-2 modified with the polymer dissolved in IPA (~13 wt%) possessing a polymer gradient. Our study presents a straightforward approach for the design of novel hygroscopic, paper-based single-layer actuators, which have a high potential for diverse soft robotic and sensor applications.

Colorimetric indicators for volatile amines based on succinic anhydride (SAh)-grafted poly (lactic acid) (PLA)

Smart materials that can undergo changes in color upon the detection of amines have the potential to provide information on the freshness of fish and meat. To engineer a material that undergoes a change in color upon exposure to biogenic amines, succinic anhydride functional groups - which are deprotonated in the presence of amines - are grafted onto a biopolymer poly(lactic acid) backbone. This material is then blended with a pH sensitive dye, yielding a material that shows a highly specific response to amines. In this system, the reaction between SAh and amines protonates the dye and leads to an irreversible change in color in the indicators. The resulting change in color was recorded and monitored with standardized photos and UV-Vis spectroscopy. Initially, indicators of different degrees of SAh (from 5 wt% to 45 wt%) grafted onto PLA were exposed to the vapours from a 400 ppm amine solution. The samples with higher degrees of grafting underwent the most visible changes in color. A more detailed study of the effect of temperature and amine concentration was performed on indicators with 30 wt% SAh. The limits of detection, half-time and kinetics of the response are also presented. Higher temperatures and concentrations were found to increase the degree of the color change while decreasing the half-time of the response of the indicators. This work shows potential opportunities for the development of simple real-time amine indicators.

Amine Responsive Poly(lactic acid) (PLA) and Succinic Anhydride (SAh) Graft-Polymer: Synthesis and Characterization

Amines are known to react with succinic anhydride (SAh), which in reactions near room temperature, undergoes a ring opening amidation reaction to form succinamic acid (succinic acid-amine). In this work, we propose to form an amine-responsive polymer by grafting SAh to a poly(lactic acid) (PLA) backbone, such that the PLA can provide chemical and mechanical stability for the functional SAh during the amidation reaction. Grafting is performed in a toluene solution at mass content from 10 wt% to 75 wt% maleic anhydride (MAh) (with respect to PLA and initiator), and films are then cast. The molecular weight and thermal properties of the various grafted polymers are measured by gel permeation chromatography and differential scanning calorimetry, and the chemical modification of these materials is examined using infrared spectroscopy. The efficiency of the grafting reaction is estimated with thermogravimetric analysis. The degree of grafting is determined to range from 5% to 42%; this high degree of grafting is desirable to engineer an amine-responsive material. The response of the graft-polymers to amines is characterized using X-ray photoelectron spectroscopy, infrared spectroscopy, and differential scanning calorimetry. Changes in the chemical and thermal properties of the graft-polymers are observed after exposure to the vapors from a 400 ppm methylamine solution. In contrast to these changes, control samples of neat PLA do not undergo comparable changes in properties upon exposure to methylamine vapor. In addition, the PLA-g-SAh do not undergo changes in structure when exposed to vapors from deionized water without amines. This work presents potential opportunities for the development of real-time amine sensors.

Superhydrophobic Hybrid Paper Sheets with Janus-Type Wettability

We introduce the design of Janus-type paper sheets where one side of the paper exhibits superhydrophobic properties, whereas the other side of the sheet remains hydrophilic and therefore can take up aqueous solutions by capillary wicking. Such papers are being prepared by chemically immobilizing a thin hybrid coating on paper sheets that consists of cross-linked poly(dimethylsiloxane) (PDMS) and inorganic particles of various sizes ranging from nanometers to several tens of micrometers. Both commercially available Whatman No. 1 filter paper and lab-engineered cotton linters-based paper substrates were treated with this approach. The hybrid paper sheets have high chemical durability, mechanical stability, and flexibility because of a covalent attachment of the particles to paper fibers and the inherent elasticity of PDMS chains. In spite of the superhydrophobicity of the coating, the untreated side of the paper substrates preserved its hydrophilicity, resulting in Janus-type wetting and wicking properties, respectively. The functionalized paper samples remained porous and permeable to gases, while possessing a gradual change in chemistry between the two sides exhibiting a dramatic wetting contrast. Such two-sided properties open up new applications for such hybrid paper materials, such as in wound dressings and/or bandages with a liquid directing and confinement ability.