Study On The Detergency Mechanisms Of Oil Stained Cotton Fibers With Confocal Laser Scanning Microscopy

With the rapid progress of detergent industry, in order to develop more efficient,cost-effective and safer detergent products，the detergency mechanisms of surfactants andenzyme in detergents needed to be examined in-depth and systematically. However, the study ondetergency mechanism lagged relatively behind, due to the multi-factors involved, such as thefabric materials, dirt composition, interactions between detergent components and otherinfluencing factors, and the lack of effective techniques of observation and characterization. Inthis paper, we used single cotton fiber as the object to be examined, and the olive oil, peanut oiland lard oil as oil stains, and used confocal laser scanning microscope to real-time monitorwashing process of oil stained cotton fiber, aimed to overcome the difficulties in observation ofwashing process and evaluation of washing effects. And the detergency mechanisms ofsurfactants and enzyme in detergents were revealed through in-depth analysis of dynamicfluorescence images and fluorescence intensity changes with scientific data processing. Thiswork had an important significance for low-temperature washing and the development of novelenzyme detergent.Firstly, the properties of the main components in detergents were examined, including thefollowings:(1) the critical micelle concentration (CMC) of sodium dodecyl benzene sulfonate(LAS) was evaluated by synchronous fluorescence spectrometry, and the results showed thatCMC1was1.50mmol/L and CMC2was6.30mmol/L;(2) the effects of temperature, pH valueand low concentrations surfactants on lipase activity based on the determination of lipase activitywas explored, and the results showed that the optimal temperature was40℃with pH=7.7, andcompared to the non-ionic surfactants (AEO-7), anionic surfactants (LAS) in low concentrationshad the weakest inhibitory effect on lipase activity.Secondly, on the basis of the above study results, the washing process of three oils (olive oil, peanut oil, lard oil) soiled on cotton fiber was real-time monitored by the means of confocal laserscanning microscope at room temperature, and the detergency mechanisms of the surfactant LASand lipase (500ppm) were discussed respectively. The results showed that it was evident from thecaptured image series that the different kinds of soiling were removed with different mechanismsby the surfactant LAS, depending on the composition and the fluidity of the lipid. Roll-up wasthe main mechanism when removing olive oil by the surfactant LAS from the fiber surface dueto the good fluidity of olive oil; emulsification was the main mechanism when removing peanutoil by the surfactant LAS from the fiber surface, because the content of unsaturated fatty acids inpeanut oil component was lower than olive oil and peanut oil had less liquidity; In addition toemulsification, solubilization of surfactant LAS, it also needed to increase repulsion between thefiber surface and lard oil to attain the goal of completely removal of stains with the help ofadding anion surfactant LAS, it was because that lard is solid at room temperature and has thehigher adhesion strength on fiber surface. The detergency mechanisms of three oils by lipasewere basically the same, the oil was broken down into glycerol esters, glycerine esters, glycerineand fatty acid soluble in water by hydrolysis during the washing process.Based on the above detergency mechanism, the washing process of peanut oil and lard oilsoiled on cotton fiber was real-time monitored by the means of confocal laser scanningmicroscope at room temperature, and the effect of washing conditions on washing effect wasdiscussed. The results showed that the surfactant LAS concentration has the greater impact onthe washing effect, with the increasing concentration of surfactant LAS, the effect of emulsionpackages and solubilization on stains was strengthened and the washing effect was enhanced;Temperature also has an important impact on the washing effect, as washing temperature rising,the emulsification and solubilization capacity of surfactant LAS was increased. On the otherhand the thermal motion of oil molecules was faster, the bonding fastness between oil stains andfiber surface was lower, which led to oil stains fallen off easily from the fiber surface. In addition,it showed that the commercial detergent B and A had the better washing effect by fluorescenceanalysis.Finally, with the application of Box-Behnken model, we explored the effect of various washing conditions on the washing effect of olive oil soiled on cotton fabric surface andoptimized the best washing conditions by response surface. The results showed that whendetergent concentration was0.60g/L, lipase concentration was4.37g/L, washing temperature was25℃, washing liquid pH=7.3,the wetting time was0.51s after washing and had the optimalwashing effect. The optimization results had an important guidance for the selection of the ratioof enzyme-containing detergent components and the range of the actual low-temperaturewashing conditions.