Study On The Preparation And Performance Of Heat-resistant And Hydrophobic Polyorganosiloxane Coating

Hydrophobic coatings have attracted a lot of interest in the scientific community owing to their non-stick performance,low surface energy,low coefficient of friction,easy sliding,outstanding hydrophobicity etc.Owing to their non-stick properties or easy removal of stuck substances,the coatings have been applied in many fields such as cooking,building,ship antifouling etc.The hydrophobic coatings require heat-resistance and solvent-resistance due to their long-term use in temperatures above 180? and exposure to corrosive solvents during use.Therefore,it is ensured that the coatings have high thermal decomposition temperature and high chemical resistance.Polysiloxane coating is formed from the hydrolysis,condensation and curing of siloxane.It is good heat-resistance hydrophobic coating,because of low curing temperature,high bond energy of Si—O bond,higher heat resistance,outstanding resistance to chemical corrosion and good dimensional stability accounting for cyclic and polycyclic Si—O—Si cross-linking structure.However,the shielding groups of siloxane monomers are less and the coating's hydrophobic property is limited.Thus the hydrophobic silicone oil is added to improve the hydrophobic properties of the coating,but the effective time is short.In order to develop polysiloxane coating with heat-resistance and permanent hydrophobic properties,a new siloxane reagent was designed and synthesized to prepare polysiloxane coating for cooking utensils application.Furthermore,a superhydrophobic coating with micro/nano roughness structure with lotus leaf super-hydrophobic was prepared under the rough surface hydrophobic theory.The details are summarized as follows:(1)?-heptamethyl-trimethoxysilyl-ethyl-trisiloxane(A0801)with reactive methoxy functional groups and polydimethylsiloxane(PDMS)hydrophobic structure was synthesized by the hydrosilylation of heptamethyltrisiloxane(MDHM)and vinyltrimethoxysilane(VTMS)at the presence of chlorine platinum sour isopropyl alcohol solution as catalyst.The structure of A0801 was characterized by GC-MS,NMR,FT-IR.The optimal synthesis conditions of A0801 is that the dosage of catalyst is 94?156 ppm of the mass of raw material,the mole ratio of MDHM and VTMS is 1.5:1,reaction temperature is 45? and time 60min which led to the high yield of hydrosilylation 86.5%?87.7%.(2)Polysiloxane coatings with heat-resistance and permanent hydrophobic properties were fabricated by nano-silica(SiO2)sol as the core with A0801 and trimethoxysilane(TMOS)as the crosslinking and hydrophobicity components under hydrochloric acid as the catalyst.The optimal preparing condition of polysiloxane coating is that the mole ratio of A0801 and TMOS is 4:1,reaction temperature is 60?,reaction time is 150min and the mass ratio of polysiloxane sol and isopropyl alcohol is 1:1.The structure and properties of the polysiloxane coatings were characterized by FT-IR,TGA,SEM,AFM,CA.Results indicated that the coating surface is smooth and the coating hydrophobicity is determined by the low surface energy.After handling in boiling water,boiling oil and calcining at 300? for a long time,the coating still exhibits excellent non-stickiness.(3)The curing reaction mechanism of the polysiloxane coating is studied through the influence of wettability and variation of functional groups' absorbance peak in heating FT-IR spectrum under different curing temperatures and time.The results indicated that the higher the temperature,the shorter the curing equilibrium time.Lower curing temperature led to easier formation of polycyclic Si—O—Si structure,which is helpful to improve the thermal stability of polysiloxane coating.(4)The super-hydrophobic polysiloxane coating was prepared by nano-silica(SiO2)sol as the core;A0801 and trimethylchlorosilane(TMCS)as the crosslinking and hydrophobic component under the catalysis of hydrochloric acid which is the hydrolysis product of TMCS.The optimal preparing condition is that the mole ratio of A0801 and TMCS is 6:1,reaction temperature and time is 30? and 60min,the mass ratio of polysiloxane sol and isopropyl alcohol is 1:1.The structure and properties were characterized by FT-IR,TGA,SEM,XRD,CA.At the optimal condition,contact angle with water of the super-hydrophobic polysiloxane coating reaches 141.7°.Results indicated that the silica sol's disparity is improved by A0801 and three dimensional cross-linking structure of Si—O—Si is generated,at the same time micro/nano roughness structure with lotus leaf super-hydrophobic is formed with TMCS.(5)The thermal stability of the coatings was studied under different heat treatment temperature,the results indicates that the coating after calcining at 200,300 and 400? the residual Si—OH groups continue to cross-link and the surface hydrophobic structure becomes more compact.The coating hydrophobic structure was not destroyed under 400?,the water CA of 143.2° after calcining at 200? increases to 154.7° after calcining at 400 ?.While the coating was calcined at 500 ? and 600?,the hydrophobic structure is destroyed and a completely hydrophilic and porous silica structure is formed.