AB - Surfactant residues in foam forming are related to the circulation of surfactant in the foaming process, but they may also affect the properties of the foam-formed product.
BA Fibre products and properties. Overview Fingerprint Projects 1. Abstract Surfactant residues in foam forming are related to the circulation of surfactant in the foaming process, but they may also affect the properties of the foam-formed product.
Access to Document Link to publication in Scopus. Fingerprint Dive into the research topics of 'Sodium dodecyl sulphate SDS residue analysis of foam-formed cellulose-based products'. Together they form a unique fingerprint. Altmetric -. Citations Cited By. This article is cited by 58 publications. Zabala, Sergio H. Lopera, Camilo A. Franco, Nashaat N. Nassar, Farid B. Johnston , George J. Hirasaki , and Sibani Lisa Biswal.
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The amount of water and therefore the amount of SDS was greater in the porous sheets. In the porous sheets, the measured SDS residues were also much higher than the theoretical values at every SDS dosage level also at 0. At the SDS dosage of 0. Thus, at that dose the porous sheets contained about 20 times the amount of the SDS compared to thin sheets.
The differences between thin and porous samples are due to two reasons. The first reason is obvious, i. The amount of water in the porous sheets was approximately 5-fold compared to the paper sheets. The second reason is related to the precipitation of dodecyl sulphate DS. The precipitate can attach to the fibre network during drainage. When generating foam, high shear forces in the mixing can prevent or at least reduce the precipitation.
When making paper sheets, the foam is collapsed quickly by vacuum, so the dewatering time is short, whereas in the case of porous sheets the water is removed by gravity and the dewatering time is much longer. Precipitation of dodecyl sulphate salts requires time, and therefore there are more precipitated DS salts in the porous samples compared to thin paper samples.
For the above two reasons, the measured SDS residues were much higher in the porous sheets than in the thin sheets. Figure 4 presents the measured SDS residues in the air-dried paper sheets and the oven-dried porous sheets as a function of theoretical SDS residues up to an SDS dosage of 1. The slope of the curve tells that the measured SDS residues were about threefold that of the theoretical ones. In practice, such a suspension can be foamed without adding more surfactant.
Results for the SDS dosage of up to 1. The measured residues are approximately three times higher than the theoretical residues. It is well known that alkyl sulphates precipitate as salts with divalent and trivalent cations, such as calcium, magnesium, barium and iron Milton , Miyamoto , Schmitt Anionic SDS may also interact with cationic additives.
Therefore, we wanted to investigate the effect of water hardness and temperature of the pulp as well as of the addition of cationic starch on SDS residues. SDS residues in the paper sheets were measured by the spectrophotometric determination method. The DM of the samples before drying varied between Due to the surfactant, the surface tension of water was lower than without the addition of surfactant. As a consequence, the capillary pressure between fibres should be smaller, and dewatering should be easier.
Table 2 The measured dry matter contents DM before drying of the foam-formed sheets in different preparation conditions. The effect of water hardness, temperature of the water-fibre suspension and addition of cationic starch on SDS residue. The graphs also show the calculated theoretical range for SDS residues. The curve of maximum theoretical values Theoretical max.
Looking at Figure 5 , it is apparent that SDS residue increased as the water hardness increased. These results are in accordance with the previous measurements from samples made in the same conditions see Figure 2.
The measured SDS residue was higher with the use of cationic starch than without starch addition, which would suggest that SDS is adsorbed via ion-ion interactions with cationic starch. When using lower dosages of cationic starch, the effect on SDS residue is probably lower. The results indicate that SDS can interact with cationic papermaking additives and in this way accumulate in the fibre structure. Calcium and magnesium salts of dodecyl sulphate are weakly soluble, and hence precipitate out from an aqueous solution, which is seen visually as increasing turbidity of the solution.
Figure 6 shows a microscopy picture from precipitated calcium dodecyl sulphate Ca DS 2 salt crystals in aqueous solution. Here we focus on calcium dodecyl sulphate Ca DS 2 because it is much less soluble than magnesium dodecyl sulphate Mg DS 2 Goddard , Miyamoto The solubility of Ca DS 2 increases with increasing temperature and is only 0.
The Krafft temperature i. SDS dosages varied from 0. Thus, in all the conditions where room temperature was applied, a part of dodecyl sulphate was precipitated as Ca DS 2. During the drainage, the fibres act as a barrier in which Ca DS 2 salt is retained. However, one should notice that the precipitation of dodecyl sulphate requires time. Also, the high shear forces in the mixing prevent partly the formation of Ca DS 2 precipitate. Turbidity measurement can be used as a tool to evaluate the amount of precipitated Ca DS 2 and Mg DS 2 salts in the solution.
The SDS solutions were prepared in tap water. The hardness of the tap water was 4. The turbidity and hence the amount of precipitated Ca DS 2 and Mg DS 2 salts decreased steadily when the temperature increased. Above the CMC, the solution contained surfactant molecules as free monomers and micelles. Turbidity of SDS solutions at different temperatures. The samples were prepared in tap water with a hardness of 4. This is in agreement with the turbidity measurements, in which the amount of precipitated calcium and magnesium salts were observed to decrease at the CMC of SDS.
In the conditions in which dodecyl sulphate was not precipitated out from the solution due to water hardness or when cationic starch was not added, SDS residues in foam-formed sheets appeared to follow the theoretical estimation. This would indicate that there is no chemical adsorption between SDS and softwood kraft fibres. Instead, the temperature of the pulp, water hardness, electrolyte concentration and the presence of papermaking chemicals with cationic charge may have an effect on SDS residues in foam-formed products.
This limit is only a limit of migration into food, not a limit of SDS residue. Figure 5 shows that the measured SDS residues in the paper sheets were below this level in all the tested preparation conditions when using SDS dosage of 0. It is worthy of note that SDS concentrations of process waters in pilot scale generally vary between 0.
SDS residues were measured from cellulose-based foam-formed paper sheets and porous sheets. The samples were analysed with two measurement methods, first to ensure the reliability of the measurement results, and secondly to detect whether the dodecyl sulphate DS molecules are still surface active or are they cleaved into two or more fragments cleavage of the S-O bond of DS. The ICP-OES method was used to determine the amount of sulphur present in the sample and by using solvent extraction spectrophotometry, the amount of DS was determined.
The two methods gave very similar results, which indicates that SDS is not permanently adsorbed on fibres it can easily be extracted from the fibre network with water and is not degraded during the drying phase of the product. At the same SDS dosage, surfactant residues were significantly higher in porous samples than in thin samples. The second reason is related to the precipitation of dodecyl sulphate.
When making thin samples by removing water by vacuum, the dewatering time is short. In contrast, in the case of porous sheets the water is removed by gravity and the dewatering time is much longer.
Precipitation of dodecyl sulphate DS salts requires time, and therefore there are more precipitated DS salts in the porous samples compared to thin paper samples. For the above reasons, the measured SDS residues are much higher in the porous sheets than in the thin sheets.
Our study showed that SDS residue increased as water hardness increased due to precipitation of dodecyl sulphate as calcium dodecyl sulphate Ca DS 2 and magnesium dodecyl sulphate Mg DS 2 salts, which remained in the fibre network. In these conditions, the measured SDS residues were close to the theoretical values, which indicates that SDS is not permanently adsorbed onto cellulose fibres. Increase in SDS residues was observed when cationic starch was added. This is due to the electrostatic interactions between the cationic starch and anionic SDS.
Funding statement: This article is based on results obtained in the 3-year Future Fibre Products FFP project during and Authors want to thank Prof. Al-Qararah, A. Colloids Surf. Search in Google Scholar. A — Alimadadi, M. Cellulose 23 1 — Ananthapadmanabhan, K. Bethell, D. Part 1. General features, kinetic form and mode of catalysis in sodium dodecyl sulfate hydrolysis.
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