Dynamics of the liquid transport through thin paper

Abstract

Single-use plastics, such as drinking straws, are not environmentally friendly and have recently been replaced by paper-based drinking straws to lower the environmental impact. However, straws made frompaper do not always meet the consumers expectations since the liquid penetrates into the straw and causes an impair on the mechanical material properties and therefore further development is required. In addition, the paper straw production needs improvement and optimization. The goals of this projectwere to characterize different liquids with varying properties, the paper straw material and the interaction between them with the future aim to produce paper-based drinking straws that meet the expectations of the consumers. Liquid characterization was performed by experimental methods such as measuring pH, viscosity and surface tension. To characterize the material, changes in relative humidity were investigated in relation to the cross-section thickness of paper straw material. Contact angle measurements and time-resolved in-situ experiments by confocal laser scanning microscopy,were performed to characterize the paper-liquid interactions, in terms of liquid transport through paper fibers, capillary transport of liquid through pore space and vapor diffusion through pore space. A set of experiments were performed where the paper material was conditioned to three different climates to investigate the effect and isolate the moisture transport phenomena. The liquid penetration studies were performed with water as a reference. The liquids with increased viscosity, PEG 3000 and PEG 35000 led to the conclusion that the liquid penetration was not affected. Liquids modified with an emulsifier, Tween®20, liquids containing surfactants composed of the commercial brand Yes, and liquids modified to a pH of 2 respectively 9 increased the penetration rate of liquid into the paper straw material compared to water. The penetration rate, however, decreased with the addition of NaCl or saccharose. It was found that the combination of techniques was powerful to investigate the dynamics of the liquid transport through thin paper. Further, three transport mechanisms did occur during the wetting of the paper strip samples in this work; I) transport through paper fibers, II) capillary transport of liquid through pore space and III) vapor diffusion through pore space. Capillary transport was found to be the dominant mechanism in the case of Yes, while the other modified liquids demonstrated a combination of the three mechanisms.