Microwave Synthesis And Structure-activity Study Of Organosilicon Surfactants

In recent years,with people's enhanced environmental awareness and health awareness,their demand for antibacterial textiles with high safety and low toxicity has been increasing a lot.Ester-based quaternary ammonium salt,which is a novel green cationic surfactant with excellent biodegradability,softness and antibacterial ability,has attracted people's attention a lot and gradually become an ideal substitute for long carbon chain alkyl methyl quaternary ammonium salt?e.g.D1821 and DC-5700?.Moreover,microwave technology can greatly improve the efficiency of quaternion reaction process.Energy conservation and consumption reduction have also become an important target for the improvement of organic synthesis process.In this study,microwave high-pressure technology was used in the reaction process.With the method of molecular design,double long-chain ester-containing cationic silicone surfactant(SiQC₂₁Cl)was synthesized via esterification and quaternization reaction using behenic acid,N-methyldiethanolamine and?-chloropropyltrimethoxysilane.Single-factor and orthogonal array design experiments to synthesis desired products were carried out to investigate the optimal reaction condition.And then the optimal results were determined as followed:in the first step,dosage of catalyst was 3%material mole ratio was n?behenic acid?:n?MDEA?=1.2:1,reaction temperature was 190?,reaching an average acid value of 3.98mgKOH/g after triplicate experiments;in the second step,the microwave power was 800 W,material mole ratio was n?silane?:n?ester amine?=1.2:1,reaction temperature was 170?,the amount of solvent was m?solvent?:m?raw material?=0.8:1,and reaction time was 12 h,reaching an average yeild of 96.60%after triplicate experiments.Compared with the traditional synthesis process,microwave high-pressure technology to prepare silicone quaternary ammonium salt owes shorter reaction time and higher conversion ratio.The chemical structures of the intermediates and target compounds were characterized by FTIR,¹H NMR spectra,ESI-MS,and TGA,which were consistent with the expected results.And the purity of the product was confirmed to reach 98.77%by HPLC-ELSD.Based on the optional synthesis process in the previous study,a series of medium/long-chain fatty acids were selected to prepare double long-chain ester amine?DCEAC_n,n=9,11,13,15,17?and long-chain ester-containing silicone quaternary ammonium salts?SiQC_nCl?.Moreover,the basic physicochemical properties of SiQC_n Cl in aqueous solution,such as surface tension,critical micelle concentration,solubilization,emulsification,wettability and foaming properties,were systematically studied.The values of CMC decreased with the increasing alkyl-length of SiQC_nCl at 25°C and so did the corresponding surface tension(?_CMC).The maximum excess surface concentration(?_max)increases with the increasing length of carbon chain.On the contrary,the area occupied by each molecule at the interface decreases under saturated adsorption.Their aggregation behaviors in aqueous solutions were also investigated systemically through transmission electron microscopy?TEM?and dynamic light scattering?DLS?.Spherical or ellipsoidal-like aggregates with diameters ranging from 300 nm to 900nm were observed,of which the particle size increases with the increasing length of the carbon chain.The bactericidal activities of SiQC_n Cl were evaluated by the method of MIC and MBC tests against Gram-positive bacteria?S.aureus?and Gram-negative bacteria?E.coli?,respectively.The results show that the antibacterial effect of SiQC_nCl on S.aureus was stronger than that on E.coli.And with the carbon number n=15,cationic silicone surfactant owns the best antibacterial activity,which is equivalent to that of D1821.The primary biodegradability of various surfactants was investigated in accordance with the National Institute of Standards?GB/T 15818-2006?.The results indicate that SiQC₂₁Cl and SiQC₁₅Cl both show better primary biodegradability than that of D1821?19.3%?and DC-5700?40.2%?,with a degradation rate of 80%after 120 h in the degrading culture cycle.Nonionic surfactant isomeric alcohol ethoxylates?1310?were used for the emulsification process of SiQC_nCl,and then the softness,whiteness and antibacterial properties of the treated cotton fabrics were determined.The results show that compared with the raw fabrics,the softness of SiQC_nCl treated cotton fabrics improves with the increase of hydrophobic tail chain,with SiQC₁₇Cl treated cotton fabrics as the best.And after five treatments,the softness of which is reduced to 77 mN and the handle is similar to D1821.Besides,SiQC₁₅Cl treated cotton fabrics show best whiteness and the anti-yellowing rate after five treatments was96.39%,which is similar to D1821.Moreover,SiQC_nCl treated cotton fabrics all show certain antibacterial ability,with SiQC₁₃Cl as the best.The morphological structure of treated cotton fabrics were observed using SEM.The results show that the surface of raw cotton fabrics was much rougher and there were more wrinkles on the surface.Moreover,the surface of SiQC₁₅Cl and D1821 treated cotton fabrics becomes smoother and the folds are relatively reduced.The reaction mechanism of the fabric finishing was predicted in this study.Crosslinking condensation of silicon methoxy between molecules,hydrogen bonding,Van der Waals forces,and electrostatic interactions are formed between cotton fabrics and the cationic silicone softener,which strengthen the intermolecular force,graft onto the surface of cotton fabrics,reduce the friction coefficient,and improve the handle of cotton fabrics.