Improvement of washing properties of liquid laundry detergents by modification with N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate sulfobetaine

Abstract

Detergency of commercial liquid detergents before and after modification with SB3C16 (5%, m/m) sulfobetaine (N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate) was examined using colorimetric analysis based on a CIELab system. The EMPA 101 standard cotton fabric soiled with carbon black and olive oil was used in washing tests under the following experimental conditions: the concentration of liquid laundry detergents 1.25–50 g/L, 30 min washing cycle, water hardness 5.35 mval/L, 40℃, 200 rpm. Results of physicochemical analysis of color, form, odor, pH, viscosity, density and content of anionic surfactants in detergents, as well as construction parameters of tested cotton fabrics, showed compliance with the requirements of standards and manufacturers’ declarations. The studies revealed that increasing the concentration of laundry detergent solutions caused a gradual increase in foaming power and detergency. Modification with SB3C16 positively improved washing ability and the maximum values were achieved at 23.7% (m-L1, 50 g/L) and 37% (m-L2, 40–45 g/L), respectively. Detergency efficiency was improved by 6.86% (m-L1) and 10.72% (m-L2) on average. EMPA 101 fabrics before and after washing were subjected to microscopic observations, which showed no serious damage to the fibers, but only slight loosening of individual fibers. In summary, the results clearly indicate that SB3C16 sulfobetaine favorably improves washing performance and can be successfully used in liquid laundry detergents due to its good surface properties.

Keywords

detergency quality liquid laundry detergents surfactants zwitterionic sulfobetaine SB3C16 colorimetric analysis

Currently, many liquid laundry detergents have been offered in the household chemistry sector. The demand for these products is increasing due to good washing properties and environmentally friendly ingredients. The most important are surfactants, which are used as emulsifiers and as wetting, suspending, solubilizing, and stabilizing substances due to their amphiphilic properties. The most commonly used are anionic, nonionic, and cationic compounds. However, another group of surfactants, such as amphoteric ones, deserves attention and can be successfully used as an additive to liquid detergents. For comparison, they are generally characterized by gentleness to eyes and skin, very low toxicity, biodegradability, better foam stability and water solubility, emulsification, salt tolerance, temperature stability, resistance to hard water and degradation by oxidation and reduction, and good detergency.^1–4 Their physicochemical properties result from the molecular structure, such as number and length of hydrophobic chains, nature and number of charged head groups, and charged spacers between negatively and positively charged head groups.⁵ The content of negatively and positively charged hydrophilic groups has an effect at high dipole moments for amphoteric active agents with intermediate hydrophilicites between nonionic and ionic surfactants.⁶ Because of these useful properties, zwitterionic compounds are often combined with anionic or cationic surfactants in many household products.⁷ The ability to strongly interact or form complexes with anionic surfactants is important in industrial applications. Currently, anionics are the main ingredients used in detergents due to their good washing and foaming properties, and moreover, zwitterionics are able to act with them as effective boosters. Studies on various properties of mixed ionic and nonionic surfactant mixtures have been widely demonstrated in the literature.^8,9

An important group of zwitterionic surfactants are betaines, which manufacturers use as boosters in hair conditioners or shampoos, because of their ability to stabilize foam.¹⁰ They are able to reduce interfacial tension to very low values in a wide concentration range (0.005–0.3%) due to their high activity at the interface.^11–13 Among betaines, sulfobetaines having sulfonate and amino groups in their structure can be distinguished. There are several subgroups with different hydrocarbon chain length and structure separating the quaternary ammonium center from the sulfonate group.¹⁴ Sulfobetaines exhibit high surface activity and have amphoteric properties at all pH values, and therefore are able to adsorb onto charged surface at all pH values without creating a hydrophobic layer.¹⁵ According to the literature, they are used in many industries related to fabrics, adhesives, flocculants, coatings, dispersants, protective colloids, shampoos, hair conditioners, detergents, and so on.¹⁶

In this study, zwitterionic sulfobetaine N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (SB3C16) has been examined as an additive to liquid laundry detergents for washing properties. In addition, the physicochemical properties of detergents and construction parameters of tested cotton fabrics have been determined. The interaction of SB3C16 with other surfactants and auxiliary components has not been studied and reported so far. Therefore, it seems justified to examine the synergistic effect of the combined substances to show negative or positive changes in detergency.

Materials and methods

Materials

Liquid laundry detergents used in these studies were selected on the Polish market due to their price category: cheap (L1) and expensive (L2). The composition and prices are shown in Table 1.

Table 1.

Compositions of tested commercial liquid laundry detergents

Liquid laundry detergents	Compositions based on manufacturers’ information	Retail gross price range of detergents (euro/L)
L1	5–15% ethoxylated (EO 9) fatty alcohol (C₁₂–C₁₈), 5–15% sodium lauryl (C₁₂–C₁₄) ether (EO 2) sulfate, 5–15% soap, <5% phosphates, enzymes, fragrance (benzyl salicylate, hexyl cinnamal, butylphenylmethylpropional), preserving agents (1,2-benzisothiazolin-3-one, 2-methyl-4-isothiazolin-3-one)	1.7–2.0
L2	5–10% sodium dodecylbenzenesulfonate, 1–5% sodium dodecylpoly(oxyethylene) sulfate (C₁₄H₂₉NaO₅S), 1–5% (C₁₀–C₁₆)alkyl benzenesulfonic acid - monoethanolamine salt, 1–5% ethoxylated (EO 7) fatty alcohol (C₁₄–C₁₅), <1% hexyl salicylate, phosphonates, soap, enzymes, preserving agents (1,2-benzisothiazolin-3-one, 2-methyl-4-isothiazolin-3-one), fragrance (α-isomethylionone, butylphenylmethylpropional, citronellol, geraniol, linalool)	3.6–3.9

In these experiments, the tested liquid laundry detergents were modified with the amphoteric surfactant: sulfobetaine N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (formula C₂₁H₄₅NO₃S; abbreviation SB3C16; molecular weight 391.7 g/mol; topological polar surface area 65.6 Å²; melting point 242℃; flash point 110℃; solubility in water 25 g/L) in the amount of 5% m/m (0.0128 mmol/L), the concentration of which is below the critical micelle concentration (CMC) (0.029 mmol/L). Modified detergents are designated as m-L1 and m-L2 later in this article. The surfactant was synthesized in our laboratory¹⁷ based on the methodology described in the literature.^14,18 These crystalline substances were separated from the reaction mixture by a filtration process and then purified by recrystallization. Lastly, white solids (SB3C16) with high purity (99.9%) were obtained and used in the research. Thermodynamic and surface parameters at different temperatures are shown in Table 2.¹⁹ The surface tension was measured in triplicate using the drop volume method in a water thermostat control at temperature range 25–45℃ during the time between 3 and 50 min in order to achieve equilibrium. The surface tension (γ) is calculated based on equation (1)

γ = \frac{FV Δ pg}{R}

(1)

where R is the tip’s radius, Δp is the difference of the two phases, g is the local gravity acceleration, V is the volume of one drop, and F(R/V)^1/3 is a correction factor that takes into account the drop’s nonsphericity.

Table 2.

Thermodynamic and surface parameters of micellization for SB3C16 sulfobetaine¹⁹

Temperature (℃)	ΔG°_mic (kJ/mol)	ΔH°_mic (kJ/mol)	ΔS°_mic (kJ/mol × K)	–TΔS°_mic (kJ/mol)	CMC (mmol/L)
25	−35.865	−32.585	0.011	−3.280	0.029
30	−35.920	−11.213	0.082	−24.707	0.036
35	−36.680	11.854	0.158	−48.534	0.0337
40	−37.495	13.235	0.162	−50.730	0.031
45	−38.300	12.922	0.161	−51.222	0.0286

The CMC concentrations were indicated from the sudden change in the slope of γ versus Log C plot. The thermodynamic parameters of micellization (free energy ΔG°_mic, entropy ΔS°_mic, enthalpy ΔH°_mic) were calculated in accordance with equations (2) to (4)

Δ G_{mic}^{\circ} = RT \ln CMC

(2)

Δ S_{mic}^{\circ} = (δ G_{mic}^{\circ} / δ T)

(3)

Δ H_{mic}^{\circ} = Δ G_{mic}^{\circ} + T Δ S_{mic}^{\circ}

(4)

The solutions of liquid laundry detergents were prepared using deionized water at hardness 5.35 mval/L. In order to prepare water of this hardness, hydrated calcium chloride CaCl₂·6H₂O and hydrated magnesium sulfate(VI) MgSO₄·7H₂O were added to the deionized water in appropriate weight proportions according to Polish Standard PN-C-77003:1997. Moderately hard water (5.35 mval/L) was chosen because water of this hardness is used in average households in Poland. Hence, the intention was to obtain the results of tests having practical reference to the actual conditions of washing processes carried out by average users. The company EMPA Testmaterialien AG plant (Switzerland) provided cotton fabrics for this research (Figure 1): EMPA 101 (soiled with carbon black and olive oil) and EMPA 210 (patterned, bleached, without stains), which meet all the requirements of the model fabrics for detergency tests. EMPA 210 fabric was used as a reference fabric in the range of tested properties. The fabric swatches were kept at room temperature (23 ± 1℃) in dark polypropylene foil in a desiccator to ensure conditions of adequate dryness and normal pressure. Carbon particles (acting as dirt) present in the fibers are chemically inert and do not form any strong chemical and physical bonds with cotton fibers that could be an obstacle to their removal during a washing process. The carbon particle size is about 0.1 µm, and the diffusion coefficient (calculated from the Stokes-Einstein equation) is about 10–12 m²/s.²⁰

Figure 1.

Tested cotton fabrics: (a) EMPA 210, (b) EMPA 101.

Methods

Evaluation of color, form and odor, checking color uniformity of liquid laundry detergents, determining the type of emulsion, determination of density by pycnometry, pH measurements (pH meter HI 221, Hanna Instruments), viscosity using Höppler viscometer, determination of the content of anionic surfactants in samples using a direct manual two-phase titration method, determination of the linear mass of fibers by means of the segment method, textile thickness, linear density and surface mass of fabrics, water absorption, and foaming power of detergents were carried out in accordance with the literature and Polish standards.^21–32

Determination of detergency (%) was carried out using EMPA 101 cotton fabric soiled with carbon black and olive oil under the following conditions: temperature 40℃, rotational speed 200 rpm, washing cycle 30 min, water hardness 5.35 mval/L, concentration of liquid laundry detergent 1.25–50 g/L, concentration of SB3C16 added was 5% (m/m). Three EMPA 101 swatches (5 × 5 cm) were washed in laundry detergent solutions (500 ml) under the same conditions in each washing process.^33–35 After detergency processes, fabric samples were rinsed in deionized water and dried at room temperature (23 ± 1℃) for 24 h. The CIELab (CIE, Commission Internationale de l’Eclairage) color space using a colorimeter Minolta CR-300 (Konica Minolta) was applied for the color measurements. Calibration parameters for a light source D₆₅ were the following: Y = 94.0, x = 0.3174, y = 0.3330. The meaning of the system of coordinates (L*, a* and b*) is as follows: the symbol L* is the vertical coordinate of a three-dimensional system of colors, which has values from 0 (black) to 100 (white); the symbol a* is the horizontal coordinate, the values of which range from –80 (green) to +80 (red); and the symbol b* is the horizontal coordinate, the values of which range from –80 (blue) to +80 (yellow). Color coordinates are calculated according to equations (5) to (7)

L * = 116 (Y / Y_{0})^{1 / 3} - 16

(5)

a * = 500 ((X / X_{0})^{1 / 3} - (Y / Y_{0})^{1 / 3})

(6)

b * = 200 ((Y / Y_{0})^{1 / 3} - (Z / Z_{0})^{1 / 3})

(7)

where the standardized values X₀ = 94.81, Y₀ = 100.0 and Z₀ = 107.3 are associated with a theoretical ideally white specimen.^36,37

The color of two sides of each fabric sample was measured 10 times. Color differences ΔE between the sample and the reference were determined on the basis of the measured L*, a*, and b* values in accordance with equation (8)

Δ E = \sqrt{(Δ L) 2 + (Δ a) 2 + (Δ b) 2}

(8)

The differences in color change are explained in Table 3 depending on the value of parameter ΔE.³⁸ Detergency D (%) was calculated based on equation (9)

D = [\frac{(Δ E - Δ E_{1})}{(Δ E_{0} - Δ E_{1})}] \times 100 %

(9)

Table 3.

Ability of a standard observer to assess color change due to ΔE values³⁹

Values of parameter ΔE	Assessment of color change by a standard observer
0 < ΔE < 1	a standard observer cannot see the color difference
1 < ΔE < 2	only an experienced observer can see the color difference
2 < ΔE < 3.5	an inexperienced observer can see the color difference
3.5 < ΔE < 5	an observer (everyone) can see the color difference clearly
5 < ΔE	an observer can see two distinct colors

The values ΔE and ΔE₁ are related to the average color difference (degree of brightness) of the fabric sample after and before the washing processes, respectively. Parameter ΔE₀ is the average color difference of the standard unsoiled fabric sample as a reference. Detergency D(%) is the efficiency of removing soil from fabrics. The fabric swatches were observed and analyzed before and after detergency processes using an Amplival microscope (Carl Zeiss Jena, Germany) and an EVO40 scanning electron microscope (SEM) (Carl Zeiss, Germany).

Results and discussion

Firstly, the SB3C16 sulfobetaine was synthesized and then characterized by Fourier-transform infrared (FTIR) spectroscopy, ¹H nuclear magnetic resonance (NMR) and ¹³C NMR analysis. At the FTIR spectrum several peaks are observed. At the peak of 914 cm⁻¹, stretching vibration of the C–N nitrogen group is present, while in 1468 cm⁻¹ a signal from bending vibration of CH₃–(N⁺) nitrogen group is present. This corresponds to the chemical shifts observed at ¹³C NMR spectrum (δ (ppm) = 64.7, 63.0, 52.6 (2 × CH₂CH₂N)) and at ¹H NMR spectrum (δ (ppm) = 3.3, 3.24 (2 × CH₂CH₂N)). Stretching vibration of the S-O sulfonate group and asymmetric stretching vibration of the S=O sulfonate group are revealed in 1031 cm⁻¹ and 1195 cm⁻¹, respectively. Chemical shifts of carbon and hydrogen are observed in 56.2 ppm and 2.55 ppm (CH₂SO₃) of ¹H NMR spectrum, respectively. The presence of long carbon alkyl chain is shown in the peaks 2851 cm⁻¹ and 2918 cm⁻¹. These bands are present at the spectrum due to the symmetric and asymmetric methylene stretching vibration. According to the fact that the alkyl chain is long, the integral intensity of signal presented in ¹H NMR in the chemical shift 1.26–1.75 ppm (15 × CH₂) is high. This corresponds to the 15 peaks (CH₂) at the ¹³C NMR spectrum observed in the range of 31.9 to 22.7 ppm. The presence of methyl group (CH₃) bonded to the alkyl chain is shown in proton and carbon ¹H NMR spectrum in 0.88 ppm and in the ¹³C NMR spectrum in 14.1 ppm, respectively. The results obtained correspond to Viana et al.’s FTIR analysis conducted for SB3C16 sulfobetaine. They reported the following peaks at the spectra: 2944 cm⁻¹ (ν_as CH₃), 2873 cm⁻¹ (ν_sym CH₃), 2954 cm⁻¹ (ν_sym N-CH₃), 2920 cm⁻¹ (ν_as CH₂), 1465 cm⁻¹ (δ CH₂), 1378 cm⁻¹ (CH₂ umbrella mode), 1402 cm⁻¹ (δ_sym N-CH₃), 912 cm⁻¹ (ν C–N stretching), 1133–1280 cm⁻¹ (ν_as SO₂), 1038 and 1058 cm⁻¹ (ν_sym SO₂).⁴⁰ Viana et al. reported that the (ν_as CH₃) vibration is not revealed in case the packing density is larger than 10¹⁷ molecules/cm². When densities are larger than that, only a peak in 2954 cm⁻¹ associated with the ν_sym(N-CH₃) is visible. We obtained a peak in 2956.7 cm⁻¹ in our analysis and peaks present below the value are indicative of a crystalline conformation, according to Viana’s findings. The CH₂ scissoring vibration and the CH₂ asymmetric stretching linearly depend on the SB3C16 packing density. However, the CH₂ symmetric feature does not linearly depend on the SB3C16 packing density. The CH₂ wagging deformations are characteristic for the 1300–1400 cm⁻¹ region, where bands are related to the e-g and d-g conformation. The d-g conformers are only reported for packing densities larger than 10¹⁷ molecules/cm². In the 900–1000 cm⁻¹ region, the ν(C–N) stretching is noticed for packing densities greater than 10¹⁶ molecules/cm². In the 1133–1280 cm⁻¹ region, the ν_as(SO₂) bands are observed for densities lower than 10¹⁶ molecules/cm². In addition, the ν_sym(SO₂) peaks visible in 1038 and 1058 cm⁻¹ are reported for densities larger than 10¹⁷ molecules/cm². The interaction of the sulfonate group with the H₃O⁺ ion may occur; as a result a split for the ν_sym(SO₂) mode is observed.⁴⁰

Secondly, the construction parameters of the EMPA fabrics were determined and the results are presented in Table 4. Linear density of EMPA 101 before washing is equal to 126.0 den (weft) and 134.5 den (warp), and after washing is 126.5 den (weft) and 135.5 den (warp). Next, liquid detergents L1 and L2 were examined organoleptically and physicochemically before and after detergency tests. The results proved to be in line with the detergent manufacturers’ declarations regarding their properties. A slight change in smell, color, pH and density was noted after the addition of SB3C16 (5%, m/m) before the washing processes (Table 5). It seems that the resulting changes in the properties of the products after modification will be acceptable during possible commercialization in the future. The results of pH measurements of detergents before and after the washing processes are shown in Table 6. The values were estimated between 6.3 and 7.7, and the solutions met the requirements of PN-C-77060:1994 standard, because each pH value is lower than 11. In addition, it can be seen that the pH increased with increasing concentration of liquids with the addition of SB3C16. Foaming power of detergents was determined and the results are shown in Figure 2. The values increased with an increase in the time for foam whipping (60 s, 180 s, 300 s) and the concentration of detergents. It was observed that for a more complex mixture of the more expensive L2 liquid, the volume of foam produced was smaller compared with the less expensive L1 liquid. The modification reduced foaming power by approximately 2.54 ml (60 s), 1.43 ml (180 s), 1.75 ml (300 s) (L1 + SB3C16, 5%, m/m) and 5.91 ml (60 s), 4.98 ml (180 s), 4.18 ml (300 s) (L2 + SB3C16, 5%, m/m) on average. It has been reported that there is a strong correlation between foamability and detergency, and too much foam volume increase in the washing process adversely affects the amount of dirt removed.⁴¹ Thus, correlation analysis between detergency and foamability was performed in these studies (Table 7). In case of L1 solutions, calculated correlation coefficients are in the range of 0.67–0.81. Modification with sulfobetaine increased the value to 0.9, and therefore it suggests that the reduction of foam formation had a better effect on washing capacity. However, in case of L2 solutions, coefficients were in the range of 0.97–0.99 and the addition of SB3C16 did not significantly change them.

Figure 2.

Results of determination of foaming power of liquid detergents: (a) L1 and m-L1; (b) L2 and m-L2.

Table 4.

Construction parameters of tested EMPA 101 and EMPA 210 cotton fabrics

Cotton fabrics	Sample mass 5 × 5 cm (g)	Thickness (mm)	Surface mass (g/m²)	Linear mass of a single thread (g/m), tex	Relative water absorption capacity (%)	Absolute water absorption capacity (g/m²)	Mass of warp threads (g/m²)	Count of warp (pcs/cm)	Mass of weft threads (g/m²)	Count of weft (pcs/cm)
EMPA 101	0.230 ± 0.002	0.17 ± 0.01	91.05 ± 0.6	8 ± 0.001	144.2 ± 1.1	132.1 ± 1.0	54.4 ± 0.1	50	39.4 ± 0.1	43
EMPA 210	0.469 ± 0.003	0.28 ± 0.01	180.4 ± 0.3	32 ± 0.03	129.6 ± 0.8	231.5 ± 1.1	104.2 ± 0.1	27	78.2 ± 0.1	22

Table 5.

Results of organoleptic and physicochemical measurements of tested liquid laundry detergents

Properties (temperature = 23 ± 1℃)	L1	L1 + SB3C16	L2	L2 + SB3C16
Color	white, milky, opaque	white brighter, more intense	green-blue, opaque	green-blue brighter, opaque
Color uniformity	uniformly colored	uniformly colored	uniformly colored	uniformly colored
Physical state	liquid	liquid	liquid	liquid
Odor	less pleasant, slightly irritating	less pleasant, less irritating	pleasant	pleasant
Type of emulsion	O/W	O/W	O/W	O/W
pH	8.51 ± 0.03	8.87 ± 0.03	8.26 ± 0.03	8.57 ± 0.03
Density (g/ml)	1.01 ± 0.0006	0.93 ± 0.0005	1.06 ± 0.0004	0.95 ± 0.0006
Viscosity coefficient η (mPa·s)	349 ± 4.3	369 ± 4.1	186 ± 3.8	214 ± 2.0
Content of anionic surfactants (%)	6.62 ± 0.07	6.25 ± 0.17	10.28 ± 0.08	9.96 ± 0.18

Table 6.

Results of pH measurements of modified liquid laundry detergents before and after the washing processes

Concentration of washing solutions (g/L)	1.25	5	10	15	20	25	30	35	40	45	50
Modified detergents	Results of pH measurements
m-L1 before washing	6.56	6.80	6.94	6.98	6.98	7.06	7.12	7.12	7.14	7.18	7.31
m-L1 after washing	6.31	6.55	6.74	6.77	6.88	6.93	6.96	7.03	7.03	7.04	7.19
m-L2 before washing	6.77	7.11	7.50	7.63	7.39	7.45	7.57	7.54	7.52	7.61	7.65
m-L2 after washing	6.68	6.96	7.44	7.18	7.33	7.41	7.36	7.46	7.43	7.61	7.60

Table 7.

Correlation coefficients between detergency and foaming power (1.25–50 g/L)

Detergents	L1			L1 + SB3C16			L2			L2 + SB3C16
Time of foaming power tests (s)	60	180	300	60	180	300	60	180	300	60	180	300
Correlation coefficients with detergency	0.67	0.73	0.81	0.89	0.90	0.90	0.99	0.98	0.97	0.95	0.91	0.90

Detergency of liquid laundry detergents (L1, L2) before and after modification with SB3C16 (5%, m/m) has been carried out using the standard EMPA 101 fabrics. As a result of measurements of color change of EMPA fabrics before and after the washing processes, the calculated ΔE values were greater than 5. Hence, according to the classification in Table 3, the laboratory observer has the impression of two different colors and can see two distinct colors. In Figure 3, the results show that detergency increased with an increase in the concentration of detergent solutions (from 1.25 to 50 g/L). Nevertheless, carbon black and olive oil dirt has not been completely removed by any of the liquids. This type of dirt is deliberately difficult to remove to demonstrate the effectiveness of detergents in research, hence it is often used as a standard by many research centers. Detergency of 18.0% (L1) and 22.2% (L2) was observed at the greatest concentrations of 50 g/L. The more expensive L2 liquid exhibits much better washing properties in comparison with the cheaper L1 liquid. Their modification with the SB3C16 (5%, m/m) sulfobetaine caused the improvement of detergency with an increase in concentration (Figure 3). The greatest detergency performance equal to 37.08% and 36.87% was reported in the case of the modified L2 liquid at a concentration of 40 and 45 g/L, respectively. The highest result for the L1 modified solution was 23.7% (50 g/L). At the initial concentrations of both L1 and L2, the results are similar: 14.84% and 16.11% for 10 g/L, 17.55% and 16.75% for 15 g/L, respectively. The addition of SB3C16 to the solutions caused a growth of detergency by 6.86% (m-L1) and 10.72% (m-L2) on average, which means a positive effect on the efficiency of removing dirt from the tested cotton fabrics.

Figure 3.

Detergency of liquid laundry detergents (L1, L2) before and after modification with SB3C16 (5%, m/m).

The characteristic course of the detergent curves is probably related to the content of surfactants in product formulations. The first maximum detergency of washing solutions occurred at concentrations of 10–15 g/L. This range contains the amount of anionic surfactants (0.66–0.99 g/L) and falls within the CMC range in aqueous solutions (CMC of sodium dodecylbenzenesulfonate = 0.36 mmol/L; molecular weight 342.4 g/mol; the content in the range from 5% to 10% is equal to 0.000146–0.000292 mol/L range). The content of sodium dodecylpoly(oxyethylene) sulfate (CMC = 0.79 mmol/L, 0.2626 g/L; molecular weight 332.43 g/mol)⁴² was equal to the range from 0.1 to 0.75 g/L at the maximum detergency, in which range the CMC value falls. The content range (5–15%) of nonionic sodium lauryl (C12-C14) ether (EO 2) sulfate is below the CMC in this case (CMC of sodium lauryl (C12–C14) ether (EO 2) sulfate = 0.82 mmol/L at γ = 33.8 mN/m; density 1.05 g/cm³ at 20℃; molecular weight 288.38 g/mol; melting point 205.5℃), because the content in the range from 5% to 15% is equal to 0.182–0.546 mmol/L range.⁴³ At achieved maximum detergency (10–15 g/L), the content of ethoxylated (EO 9) fatty alcohol (C12-C18) (CMC = 0.015 g/L at γ = 30.5 mN/m; molecular weight 582–666 g/mol)⁴⁴ was in the range from 0.5 to 2.25 g/L, which is above its CMC. Furthermore, the content of ethoxylated (EO 7) fatty alcohol (C14–C15) (CMC = 0.0714%, 0.002075 g/mol, 0.0028 µg/L at γ = 35.05 mN/m; molecular weight 522–536 g/mol)⁴⁵ was equal to the range from 0.1 to 0.5 g/L, which exceeds its CMC values. According to Tadros, alkyl sulfates exhibit good foaming properties with an optimum at C12–C14 alkyl chain.⁴⁶ Ethoxylated fatty alcohols are able to give maximum detergency efficiency at the degree of ethoxylation equal to 5–7·mol EO.⁴⁷

The additional content of CB3C16 amphoteric surfactant was equal to 0.5–1.5 g/L in this discussed first detergency range. The conducted research indicates that the achievement of the first maximum detergency is related to the CMC values of surfactants used in formulations. According to the mechanism of the washing process, the washing solution first moistens and penetrates dirt, then surfactants adsorb on its surface and penetrate the structure. In the next stage, the liquid dirt is emulsified or dissolved, while the solid dirt is dispersed. Impurities are thoroughly surrounded by surfactants and released from the adjacent surface (rolling-up mechanism). An emulsion is created, which contains dirt bound by surfactants. At surfactant concentrations equal to CMC, dirt particles close to the maximum can be removed due to saturation of the micellar solution. This confirms the nature of the obtained dependence of detergency on the concentration of active substances in washing liquids. Other compounds present in the solution also affect the CMC value. Further increasing the concentration of surfactants improves detergency with a linearly increasing tendency. This is the result of surfactants supported by other active components present in the composition that synergistically increase the efficiency of dirt removal as the concentration increases up to 50 g/L. Probably this phenomenon is associated with the synergistic action of a large number of other ingredients that support the process.

Carbon black particles contain hydrophilic and hydrophobic groups in aqueous solution, which enables electrostatic or steric interaction with amphiphilic particles. Hydrophobic particles are more strongly attracted to the surface of cotton fiber than hydrophilic particles, probably as a result of Coulomb attraction. Removal of dirt is significantly related to the surface energy of the textile substrate. Cellulose in cotton fabrics has low surface energy (and low critical surface tension) for wetting in water, hence it is characterized by high resistance to wet soiling by hydrophobic soil, which also means easy removal during the washing processes.⁴⁸ Due to the acid–base nature of carbon black, the molecular groups present on its surface can gain or lose a proton depending on the pH of the aqueous solution. According to the results of some researchers, the isoelectric point of carbon particles in water is achieved at about pH 6.5, when the net surface charge is zero (zeta potential ζ = 0).^49,50 The surface charge becomes negative at higher pH values. In the tests, the pH of L1 and L2 washing solutions ranged from 8.26 to 8.87. At this pH, during adsorption, cationic surfactant groups were attracted by the negatively charged surface of carbon particles. Due to its properties, amphoteric sulfobetaine SB3C16 has a negative electrostatic charge at pH > 8. This means that in the washing solution SB3C16 repels negatively charged carbon black particles on fibers according to the rolling-up mechanism. Moreover, the wetting and removal of dirt from the fiber surface is supported by the low interfacial surface of SB3C16. The above considerations can probably explain the increased amount of carbon black removed after adding sulfobetaine to the wash bath.

The effects of the sulfobetaine additive (Figure 3) on the detergency of the washing powders were analyzed statistically to compare the results for samples L1 and L1 with SB3C16, and L2 and L2 with SB3C16, with a constantly increasing concentration of both types of detergents. The F-test was carried out using the significance level α = 0.05. It was found that the differences between L1 and L1 + SB3C16 (5%, m/m) are statistically different. The F value equal to 28.98 and the P value was computed at the level of 2.35402·10⁻⁶. The P value is lower than 0.05, therefore the parameter values to be compared are significantly different. The results of F-test at the 0.05 significance level showed that L2 and L2+ SB3C16 datasets are also statistically different. The F and P values were equal to 53.51 and 2.6587·10⁻⁸, respectively. The P value is lower than 0.05, thus the parameter values to be compared are also significantly different.

An optical microscope and SEM were used to evaluate the structure of fabrics and fibers before and after the washing processes. The structures of EMPA 210 (100% cotton, white, not soiled) and EMPA 101 (100% cotton, soiled with carbon black and olive oil) before the washing processes are shown in Figure 4. Weft and warp threads are woven in an orderly manner and only insignificant free single strands of fibers are visible. EMPA 101 samples after the washing processes in L1 and L2 laundry liquids before and after modification (at concentrations 1.25 and 50 g/L) are shown in Figures 5 and 6. No serious fabric damage was found in the examined concentration range at 359× microscopic approximation. On the other hand, damage in the form of delamination of individual fibers is visible in SEM images. Furthermore, it was observed with the naked eye that little pilling appeared on the fabrics after the washing processes. The main reason is the movement of the stirrer blades, rubbing against the surface of the fabric during the process. This corresponds to the results obtained by Liu et al. who suggested that the main causes of fabric wrinkling during washing were liquor ratio and the centrifugal force imposed on the fabric.⁵¹

Figure 4.

Cotton fabrics before the washing processes: EMPA 210, white, uncontaminated: (a) (359×), (b) (1346×), (c) (10,000×); EMPA 101, soiled with carbon black and olive oil: (d) (359×), (e) (1346×), (f) (10,000×).

Figure 5.

Images of EMPA 101 cotton fabrics after the washing processes at various concentrations of the L1 detergent solutions: (a) 1.25 g/L (359×), (b) 1.25 g/L (10,000×), (c) 50 g/L (359×), (d) 50 g/L (10,000×); m-L1: (e) 1.25 g/L (359×), (f) 1.25 g/L (10,000×), (g) 50 g/L (359×), (h) 50 g/L (10,000×).

Figure 6.

Images of EMPA 101 cotton fabrics after the washing processes at various concentrations of the L2 detergent solutions: (a) 1.25 g/L (359×), (b) 1.25 g/L (10,000×), (c) 50 g/L (359×), (d) 50 g/L (10,000×); m-L2: (e) 1.25 g/L (359×), (f) 1.25 g/L (10,000×), (g) 50 g/L (359×), (h) 50 g/L (10,000×).

The FTIR spectra of EMPA 101 cotton fabrics before and after washing with detergents are shown in Figures 7 and 8. Typical cellulose, lignin and hemicellulose bands are disclosed in both spectra. The following vibrations were observed at wavelengths: 3334 cm⁻¹, the stretching vibration of hydroxyl groups present in cellulose, lignin and water;⁵² 2900 cm⁻¹, C-H stretching vibrations present in hemicellulose and cellulose;⁵³ 1620 cm⁻¹, O-H vibrations of water present in the fibers;⁵⁴ 1428 cm⁻¹, CH₂ symmetric bending in cellulose; 1360 and 1315 cm⁻¹, bending vibrations of the C-H and C-O groups of aromatic rings in cellulose (polysaccharides); 1245 cm⁻¹, the stretching vibration of hydroxyl-bound carbon; 1165 and 1108 cm⁻¹, the C-O bond stretching vibration; 1053 and 1029 cm⁻¹, the C-O and O-H stretching vibrations in hemicellulose and lignin (polysaccharides); and 894 cm⁻¹, β-glycosidic connections between monosaccharides.⁵⁵ L1 and L2 detergents and those modified with SB3C16 caused a slight change in peak intensity towards higher transmittance values.

Figure 7.

FTIR spectrum of EMPA 101 before and after the washing processes using L1 detergent.

Figure 8.

FTIR spectrum of EMPA 101 before and after the washing processes using L2 detergent.

Conclusions

In this study, the influence of the addition (5%, m/m) of the amphoteric surfactant N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate sulfobetaine (SB3C16) to commercial liquid laundry detergents (cheaper L1 and more expensive L2) was demonstrated on the effectiveness of detergency. The standard EMPA 101 cotton fabric soiled with carbon black and olive oil was the material used to be tested for washing efficiency.

The construction parameters of the fabrics were determined as well as the physicochemical properties of the laundry liquids. The assessment of color, color uniformity, form, smell, pH, viscosity, density and content of anionic surfactants showed compliance with the detergent manufacturers’ declarations. The liquids’ modification with SB3C16 did not cause significant changes to these properties. A gradual increase in foaming power and detergency as the solution concentration increased (1.25–50 g/L) was observed. The first maximum detergency of both modified m-L1 and m-L2 was achieved at the range of 14.8–17.6% (10–15 g/L). The phenomenon is probably associated with CMC formation of surfactants used in formulations. The next highest detergency was equal to 23.7% (m-L1, 50 g/L) and 37% (m-L2, 40–45 g/L). This was due to the synergistic effect of the activities of all ingredients in the washing solutions. The addition of SB3C16 to the liquids was the cause of an increase in detergency by 6.86% (m-L1) and 10.72% (m-L2) on average. Microscopic analysis of images of EMPA 101 fabrics before and after the washing tests did not reveal any serious damage, but only the occurrence of pilling of individual fibers.

In conclusion, it can be stated that modifying washing liquids with the addition of the SB3C16 amphoteric surfactant has a positive effect on the efficiency of removing carbon black and olive oil from cotton fabrics. The results of this study indicate that the tested sulfobetaine can potentially be used as a component of liquid laundry detergents.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

References

Tsubone

Uchida

Mimura

. New amphoteric surfactants containing a phosphoric acid group: II. Binary system of amphoteric/anionic surfactant of sodium 2-(N-2-hydroxytetradecyl-N-methylamino)ethyl hydrogen phosphate. J Am Oil Chem Soc 1990; 67: 455–458.

Mahajan

Vohra

Shaheen

, et al. Investigations on mixed micelles of binary mixtures of zwitterionic surfactants and triblock polymers: A cyclic voltammetric study. J Colloid Interface Sci 2008; 326: 89–95.

Kamal

Hussein

Sultan

. Review on surfactant flooding: phase behavior, retention, IFT, and field applications. Energy Fuels 2017; 31: 7701–7720.

Cheng

Yang

Niu

, et al. Progress in synthesis and application of zwitterionic gemini surfactants. Front Mater Sci 2019; 248: 1–16.

Yoshimura

Ichinokawa

Kaji

, et al. Synthesis and surface-active properties of sulfobetaine-type zwitterionic gemini surfactants. Colloids Surf A Physicochem Eng Asp 2006; 273: 208–212.

Staszak

Wieczorek

Zieliński

. Synthesis and interfacial activity of novel sulfobetaines in aqueous solutions. Tenside Surfact Det 2013; 50: 45–51.

Singh

Marangoni

. Synergistic interactions in the mixed micelles of cationic gemini with zwitterionic surfactants: The pH and spacer effect. J Colloid Interface Sci 2007; 315: 620–626.

Din

Sheikh

Dar

. Interaction of a cationic gemini surfactant with conventional surfactants in the mixed micelle and monolayer formation in aqueous medium. J Colloid Interface Sci 2009; 333: 605–612.

Din

Sheikh

Dar

. Analysis of mixed micellar and interfacial behavior of cationic gemini hexanediyl-1,6-bis(dimethylcetylammonium bromide) with conventional ionic and nonionic surfactants in aqueous medium. J Phys Chem B 2010; 114: 6023–6032.

10.

Yan

. Effect of alkyl chain on N-alkyl dimethyl betaine. Appl Chem Ind 2005; 10: 622–624.

11.

Zhang

Somasundaran

. Advances in adsorption of surfactants and their mixtures at solid/solution interfaces. Adv Colloid Interface Sci 2006; 123–126: 213–229.

12.

Wang D, Liu C, Wu W, et al. Development of an ultralow interfacial tension surfactant in systems with no-alkali for chemical flooding. In: Proceedings of the 2008 Society of Petroleum Engineers/Department of Energy Symposium on Improved Oil Recovery, Tulsa, OK, 20–23 April 2008, Paper 109017..

13.

Wang D, Liu C, Wu W, et al. Novel surfactants that attain ultra-low interfacial tension between oil and high salinity formation water without adding alkali, salts, co-surfactants, alcohols and solvents. In: Proceedings of the 2010 Society of Petroleum Engineers EOR Conference at Oil & Gas West Asia, Muscat, Oman, 11–13 April 2010, Paper 127452..

14.

Ward

Davies

Hodges

, et al. Synthesis of quaternary alkylammonium sulfobetaines. Synthesis 2002; 16: 2431–2439.

15.

Staszak K, Wieczorek D, Michocka K, Effect of Sodium Chloride on the Surface and Wetting Properties of Aqueous Solutions of Cocoamidopropyl sulfobetaine. J Surfact Deterg 2015; 18: 321–328.

16.

Kabiri

Faraji-Dana

Zohuriaan-Mehr

. Novel sulfobetaine-sulfonic acid-contained superswelling hydrogels. Polym Adv Technol 2005; 16: 659–666.

17.

Wieczorek

Staszak

. Surface activity of selected sulfobetaines. Towaroznawcze Problemy Jakości 2013; 3: 124–132.

18.

Lomax

. Amphoteric surfactants, New York: Marcel Dekker Inc., 1996.

19.

Cheng

Wei

, et al. Thermodynamics of micellization of sulfobetaine surfactants in aqueous solution. J Surfactants Deterg 2012; 15: 757–763.

20.

Kalak

Cierpiszewski

. Correlation analysis between particulate soil removal and surface properties of laundry detergent solutions. Text Res J 2015; 85: 1884–1906.

21.

PN-C-77060:1994. Agents for laundering and washing – Washing powders – Requirements and methods.

22.

PN-EN 1262:2004. Surface active agents – Determination of pH of solutions and dispersions of surfactants.

23.

Jonsson UJ and Lilje KC. Elastohydrodynamic lubrication properties of polyol ester lubricants-R134a mixtures. International Compressor Engineering Conference, 1998, Paper 1227, pp.123–128.

24.

PN-C-77003:1997. Household chemistry products – Liquid agents for hand dishwashing – Requirements and tests.

25.

PN-EN 12728:2001. Surface active agents – Determination of foaming power – Perforated disc beating method.

26.

PN-ISO 2271:2000. Surface active agents – Detergents – Determination of anionic-active matter by manual or mechanical direct two-phase titration procedure.

27.

PN-P-04653:1997. Textiles – Threads – Determination of the linear mass by the segment method.

28.

PN-EN ISO 5084:1999. Textiles – Determination of thickness of textiles and textile products..

29.

PN-EN 1049-2:2000. Textiles – Methods for analyzing the structure of woven products – Determination of the number of threads per unit of length.

30.

PN-ISO 3801:1993. Textiles – Woven fabrics – Determination of mass per unit length and mass per unit area.

31.

PN-72/P-04734:1972. Textile testing methods – Determination of water absorption..

32.

PN-EN 12728:2001. Surface active agents – Determination of foaming power – Perforated disc beating method.

33.

PN-76/C-04810:1976. Agents for laundering and washing – Determination of laundering effects of enzyme powders..

34.

PN-87/C-04810/03:1987. Agents for laundering and washing – Determination of effects agents on laundering woven, woollen and woollen-like fabrics..

35.

PN-93/C-04810/01:1993. Agents for laundering and washing – Determination of effects of laundering of agents for laundering woven cotton fabrics..

36.

Berger-Schunn

. Practical color measurement: a primer for the beginner, a reminder for the expert, New York: John Wiley & Sons, Inc., 1994, pp. 97–97.

37.

Cliff

King

Schlosser

. Anthocyanin, phenolic composition, colour measurement and sensory analysis of BC commercial red wines. Food Res Int 2007; 40: 92–100.

38.

CIELab. https://pl.wikipedia.org/wiki/CIELab (2019).

39.

Rogowska

. Synaesthesia and individual differences, Cambridge University Press, 2015.

40.

Viana

da Silva

ABF

Pimente

. Infrared spectroscopy of anionic, cationic, and zwitterionic surfactants. Adv Phys Chem 2012; 1: 1–14.

41.

Karthick

Jangir

Chattopadhyay

. Foaming and cleaning performance comparison of liquid detergent formulations using mixtures of anionic and nonionic surfactants. Tenside Surfact Det 2018; 55: 162–168.

42.

Aoudia

Al-Haddabi

Al-Harthi

, et al. Sodium lauryl ether sulfate micellization and water solubility enhancement towards naphthalene and pyrene: effect of the degree of ethoxylation. J Surfact Deterg 2010; 13: 103–111.

43.

Ćirin

Poša

Krstonošić

. Interactions between selected bile salts and Triton X-100 or sodium lauryl ether sulfate. Chem Cent J 2011; 5: 89–89.

44.

Kosswig K. Surfactants. In: Ullmann’s encyclopedia of industrial chemistry. Weinheim: Wiley‐VCH Verlag GmbH & Co. KGaA, 2000, pp.1–505..

45.

Jadidi

Adib

Malihi

. Synergism and performance optimization in liquid detergents containing binary mixtures of anionic–nonionic, and anionic–cationic surfactants. J Surfact Deterg 2012; 16: 115–121.

46.

Tadros

. An introduction to surfactants, Walter de Gruyter GmbH, 2014, pp. 1–235.

47.

Cahn A. Proceedings of the 3rd world conference on detergents: global perspectives. AOCS, 1994, pp.1–280.

48.

Slade

. Handbook of fiber finish technology, New York: Marcel Dekker, Inc., 1998.

49.

Jada

Ridaoui

Donnet

. Modification of carbon black surface charge and size by molecular and macromolecular surfactants adsorption. Colloids Surf A Physicochem Eng Aspects 2006; 278: 149–159.

50.

Lau

Furlong

Healy

, et al. The electrokinetic properties of carbon black and graphitized carbon black aqueous colloids. Colloids Surf 1986; 18: 93–104.

51.

Liu H, Wang Y, Gong RH, et al. The relationships between washing parameters, fabric movement, and wrinkling in a top-loading washer. Textile Research Journal 2018; 88: 1367–1376.

52.

Tomczak

Satyanarayana

Sydenstricker

. Studies on lignocellulosic fibers of Brazil: Part III – Morphology and properties of Brazilian curauá fibers. Compos Pt A-Appl Sci Manuf 2007; 38: 2227–2236.

53.

Satyanarayana

Guimarães

Wypych

. Studies on lignocellulosic fibers of Brazil. Part I: Source, production, morphology, properties and applications. Compos Pt A-Appl Sci Manuf 2007; 38: 1694–1709.

54.

De Rosa

Kenny

Puglia

, et al. Morphological, thermal and mechanical characterization of okra (Abelmoschus esculentus) fibers as potential reinforcement in polymer composites. Compos Sci Technol 2010; 70: 116–122.

55.

Romanzini

Ornaghi

Jr Amico

, et al. Preparation and characterization of ramie-glass fiber reinforced polymer matrix hybrid composites. Mater Res 2012; 15: 415–420.