Laboratory data on dynamics of microplastic particles sinking in seawater with dispersed xanthan gum and kappa-carrageenan and rheological properties of these dispersions

This paper presents a dataset comprising measurements of the sinking dynamics of microplastics settling in artificial seawater (AS) and in dispersions of polymers in seawater: xanthan gum, kappa-carrageenan, and their mixtures in two concentrations: 0.5 g/L and 1 g/L. Plastic particles are classified into fifteen groups representing various shapes: disks, rods, blades, spheres, and materials: PS, POM, PET, PA6. The sinking of individual particles in a settling tank was visualized using the shadowgraph method and images were recorded using a camera with macro lenses. Next, Particle Tracking Velocimetry was applied to retrieve the time-resolved position of MPs and their orientation and to calculate instantaneous sinking velocity. Non-Newtonian properties of solutions were measured using a rheometer. Shear-dependent viscosity, shear stress amplitude sweeps, the first normal stress difference, and gelling time were assessed. Datasets may find application in a range of scientific and engineering areas including fluid mechanics, chemical engineering, food engineering, petroleum industry, wastewater treatment, rheology, and environmental hydrodynamics, e.g. in research on particle dynamics in complex fluids, modeling of microplastics fate in aqueous systems, and to develop numerical models on the hydrodynamics of solid particles in complex liquids.

microplastics fate in aqueous systems, and to develop numerical models on the hydrodynamics of solid particles in complex liquids. ©

Value of the Data
• Dataset is useful in understanding the impact of polysaccharides on the rheological properties of seawater and the effects of polymer mixtures on the rheology of electrolyte solutions.
• Dataset provides new observations on the non-Newtonian effects in settling dynamics of solid particles of various shapes.• Data may be useful for researchers investigating physio-chemical properties of non-Newtonian fluids and settling of solid particles in these systems representing the fields of chemical engineering, rheology, food technology, petroleum engineering, pharmaceutical industry, wastewater treatment, environmental sciences, marine sciences, and environmental pollution.• This dataset may be used to develop numerical models on sinking dynamics of regular and irregular solid particles in non-Newtonian fluids.• The dataset may be useful from the viewpoint of marine chemistry, oceanology, and marine sciences since it presents unique measurements of seawater properties modified by natural polymers.• Data may be used to model the fate of microplastics and other solid particles in marine waters with excessive exopolymers.

Background
This dataset was collected within laboratory research on the effects of excessive amounts of exopolymers (EPSs) on the rheology of seawater and implications for settling dynamics of microplastics (MPs) in marine environments [2] .Field studies have already demonstrated that EPSs secreted in excess form a gel-like network during algal blooms [3] that transform seawater into rheologically complex liquid [4][5][6] .However, the rheological effects of such modified marine systems on physical, biological, and chemical processes are not well understood [ 7 , 8 ] and the dataset represents significant input into this field of research.The laboratory procedure and data will help other research groups study the rheology of biologically modified seawater and MPs transport.
Moreover, the data can be used in a wide range of research and engineering problems involving complex fluids and settling dynamics of solid particles including wastewater treatment technology, food processing, petroleum industry [9] .Widely used commercial polysaccharidesxanthan gum and κ-carrageenan, have been selected in this study to demonstrate their impact on the rheological characteristics of electrolyte solutions, which is a problem of practical importance.

Data Description
The data present measurements from seven experiments on MPs settling in artificial seawater and seawater with the addition of polysaccharides: xanthan gum, κ-carrageenan, and their mixtures.In settling experiments, data on the time-resolved position of particle centroid and orientation was collected.Moreover, each test solution was measured for its rheological properties.

Dimensions of Particles
The dataset collected in the Dimensions_of_particles folder comprises dimensions of test MPs measured for samples containing a few to over one hundred particles.Thus, the folder contains 14 .csvfiles MPType_MPSub-Type .csv, where MPType indicates (S -sphere, D -disk, R -rod, B -blade, I -irregular), MPSub-Type is a sub-type of particle (a, b, c) if more than one kind of MP is considered in terms of dimensions for a given shape.These data were next used to calculate the average dimensions of MPs collected in Table 1 .Dimensions were not measured for one particle type, S_PS, since they were provided by the manufacturer.

Settling Experiments
Dataset from settling experiments collected in the Settling_experiments folder comprises time-resolved horizontal, and vertical coordinates of MP centroid and time-resolved orientation of microplastic particles.Fig. 1 presents the scheme of data organization.
Each of the seven sub-folders NameOfExpSet comprises data for a separate experimental set dedicated to a test solution.Folders are named after solution type referred to as AS_POLC with AS indicating artificial seawater; POL indicating polymer type: XG -xanthan gum, CRκ-carrageenan, and XGCR -a mixture of xanthan gum and κ-carrageenan; C stands for the concentration of polymer which is 0.5 or 1 g/L.
Each sub-folder contains n .csvfiles, where n is the number of runs in the experiment, AS_ POLC _MPType_MPSub-Type _run_ Run .csv, where MPType indicates (S -sphere, D -disk, Rrod, B -blade, I -irregular), MPSub-Type is a sub-type of particle (a, b, c) if more than one kind of MP is considered in terms of dimensions for a given shape (see Table 1 for definitions).R un denotes the number of runs for a particular MPType and MPSub-Type in the experimental set.In files, data are organized in four columns: x [pix], z [pix], t[s] , and angle[degrees] where x and z are horizontal and vertical coordinates of MP centroid, t is a time instant, and angle indicates an angle between the x-axis and the major axis of the ellipse that has the same second-moments as the particle projection assessed using Matlab Image Processing Toolbox®.

Rheology
Rheological measurements collected in Rheological_data comprise flow properties, viscoelasticity, and determination of gelling time.Fig. 2 presents a scheme for the organization of these data.Flow properties data are stored in the flow_data folder, viscoelasticity data in the ampli-tude_sweep folder, and data on gelling in the gelling_time folder.Each of these three folders contains .csvfiles named using the AS_POLC convention explained in section 1.1 with respec-

Experimental Design, Materials and Methods
Settling dynamics of fifteen groups of microplastic particles settling in artificial seawater (AS) and in dispersions of polymers in seawater: xanthan gum (XG), κ-carrageenan (CR), and their mixtures (XG + CR), were carried out and accompanied with rheological measurements of test solutions.

Materials
Seven types of solutions were prepared based on artificial seawater comprising NaCl, MgCl2, Na2SO4, CaCl2, KCl, NaHCO3, KBr, H3BO3, SrCl2, NaF.Artificial seawater was prepared according to ASTM standards [10] that specify types and amounts of salts comprising standard seawater of salinity 3.5%.Analytical-grade polysaccharides: xanthan gum (XG, Sigma Aldrich CAS: 11138-66-2) and κ-carrageenan (CR, Sigma Aldrich CAS: 11114-20-8), were used to get a solution of 0.5 g/L and 1 g/L of each polysaccharide and a mixture of the two polysaccharides in 4:1 proportion.First, polysaccharides were added to 1L of distilled water to get a well-hydrated and dissolved solution.Next, each of them was mixed with a 1L solution of salts comprising AS, and distilled water was added to obtain a designated volume of solution ( Fig. 3 ).Fifteen groups of particles varying in shape and material were studied in the experiments: three sets of disks, four sets of rods, two sets of blades, three sets of spheres, and three sets of irregular particles.Particles were composed of plastic materials: PA -polyamide 6, POM -polyoxymethylene, PS -polystyrene or polystyrene divinyl benzene, and PET -polyethylene terephthalate with densities and dimensions specified in Table 1 .Irregular particles and spheres were industrial beads, while other shapes were manufactured in the laboratory from foils (disks and blades) and fibers (rods).In each settling experiment, a few replicate particles from the same group were tested.

Settling Experiments
Settling experiments were performed in the Laboratory of Hydrodynamic Micromodels, Institute of Geophysics, Polish Academy of Sciences.Experiments were performed in a transparent tank with an inner cross-section of 0.11 m x 0.11 m and a height of 0.5 m.After filling the tank with a test solution, a temperature was controlled using a liquid thermometer with an accuracy of up to 0.1 • C to exclude convective motions in the liquid.A series of a few replicate particles from each group were released to the tank using a tweezer.Particles were introduced beneath the surface of the test liquid one by one with at least a 3-minute interval between tests to let the solution relax.
The shadowgraph method was used to visualize sinking particles by illuminating the back of the tank with an LED panel.Images of sinking particles were acquired using a monochromatic Basler camera acA2500-60um with Schneider-Kreuznach macro lenses Componon 2.8/28-001 with aperture 3.5 F and 6 mm extension tube operating at 2590 × 2048 resolution and one pixel corresponding to 31 μm.Images were captured with frequency varying between 20 and 90 fps depending on the rate of sinking process for each particle.
Acquisition parameters were controlled using the digital video camera recording software StreamPix®.Images recorded directly on the disk of a computer were manually selected to remove any low-quality or incomplete datasets.Retained images were cropped to decrease the volume of images.Next, they were converted into a binary mode using thresholding available in Matlab®, and particles were identified in the images.In the next step, the centroid and angle (angle between the x-axis and the major axis of the ellipse that has the same second-moments as the particle projection) using Image Processing Toolbox® in Matlab® were identified.

Rheological Tests
Rotational rheometer Physica MCR301 was applied to measure the rheological properties of test solutions at the Department of Inorganic Chemistry of Warsaw University of Technology.Measurements were performed in a coaxial cylinder measuring geometry (CC17-SN12952, 0.714 mm gap), at a temperature of 21 °C.Flow properties were captured in a controlled shear rate mode in the shear rate ranging from 0.1 to 100 s −1 .The first normal stress difference was calculated using a modified version of the Cross equation.Amplitude sweeps were recorded in small strain oscillatory tests at a constant frequency of 1Hz with shear stress amplitude ranging from 0.0 0 0 01 Pa to 20 Pa.In the gelling test, an initial shear rate of 100 s −1 was applied for 60 s and then the sample was relaxed for 120 s.A constant shear stress of 0.001 Pa was abruptly applied to record the resultant shear rate.

Limitations
Not applicable.

Fig. 1 .
Fig. 1.Schematic structure of data produced in settling experiments, n is the number of runs in an experimental set.
2024 The Authors.Published by Elsevier Inc.This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ ) ×0.11m inner dimension) with transparent walls and backlight.Basler acA2500-60um camera with Schneider-Kreuznach macro lenses Componon 2.8/28-001 with aperture 3.5 F mounted perpendicular to the front wall of the tank was used to capture images of particles settling in test solutions.Data were recorded by digital video camera recording software StreamPix®.ImageJ and Matlab® Image Processing Toolbox® enabled data pre-processing and processing, and next the assessment of time-resolved microplastic centroid position and orientation.

Table 1
Physical properties of test microplastic particles: length, breadth, and thickness (provided as mean values).