Preparation Of Transparent PU-g-PDMS Coatings Using AC-Starch As Polyol

Polyurethane(PU)has excellent properties and broad application prospects.Development of biodegradable PU is of great significance for the sustainable development of materials.The transparent anti-smudge PU coatings can be prepared by the nano-pools of a grafted lubricating ingredient for de-wetting enablement(NP-GLIDE)method,but the raw materials of polyols are unrenewable because it is obtained from petrochemical industry.Herein this work,environmentally friendly bio-based transparent omniphobic PU coatings have been successfully prepared with NP-GLIDE method by using bio-starch as polyol,whose solubility was improved by acetylation modification,hexamethylene diisocyanate trimer(HDIT)as crosslinking agent,and a small amount of monocarbinol terminated polydimethylsiloxane(PDMS-OH)as functional lubricant component which is polyol too.This kind of coating has broad application prospects on the surfaces of various substrates such as wood,metal,and glass.The main works of the thesis are as follows:1.Preparation and characterization of ac-Starch.Ac-Starch was prepared by acylation using liner starch and acetic anhydride as raw materials,glacial acetic acid as solvent,and methanesulfonic acid as catalyst.Effects of raw material ratio and reaction time on the degree of acylation and solubility of the products were investigated in detail.The products were characterized by IR and 1H-NMR.Results showed degree of acylation of acetylated starch reached 88.33%which was prepared at the optimal conditions:molar ratio of starch sugar unit to acetic anhydride 1:3,reaction time 24 h.2.Preparation and characterization of PU transparent coatings.PU coatings were prepared by using ac-Starch and HDIT(molar ratio of-NCO and-OH is 1.2:1.0)as raw materials on the glass.Transmittance of coatings was measured at 500 nm using UV spectrophotometer.Effects of solvent type,pre-reaction time and dilution ratio of the pre-reaction solution on light transmittance of the coatings were investigated.The free-NCO regression during the pre-reaction process(3 h)were tracked by IR.Results showed that all coatings with transmittance higher than 97%can be gotten at the optimal conditions:mixed solvent(VDMF:MEK:DMC=1:2:6),pre-reaction time 3 h,dilution ratio 1:3.3.Preparation and characterization of PU functional coatings.PU functional coatings were prepared using ac-Starch as a polyol,HDIT as a crosslinking agent(n-NCO:n-OH=1.2:1.0),and a small amount of PDMS-OH as a functional component.(1)Effects of contents of PDMS-OH(0.5,1.0,2.0 and 3.0 wt.%)on transmittance,hardness,silicon atom abundance,water contact angle(WCA)and sliding angle(WSA)of PU functional coatings(denoted as PU-g-PDMS0.5,PU-g-PDMS1.0,PU-g-PDMS2.0,PU-g-PDMS3.0)were studied in detail.Results showed that transmittance of all coatings exceeds 97%,hardness level of the pencil reaches 3H.As the amount of PDMS-OH increases,abundance of silicon atoms in the coatings and WCA value increases,but the WSA and contact hysteresis value(Δθ)decreases.(2)Contact angle(CA)and sliding angle(SA)of both immiscible solutions(hexadecane,THF,dodecane,decadecane)and miscible solutions(water,diiodomethane,DMF,ethanol,methanol)with PDMS on PU-g-PDMS2.0 coating were measured.Results showed that the lower surface tension of the test liquid is,the CA become smaller.The SA values of miscible solution with PDMS were lower than that of immiscible solution.(3)Anti-smudge performance of the PU-g-PDMS coating was tested by inks(marker marks),water-based(water,milk,coffee,and ink)and oil-based(hexadecane)contaminants.Results showed that the ink marks drawn on the coating surface by a marker were shrunk,and the area occupied by the shrunk ink decreased as the content of PDMS-OH in PU-g-PDMS coating increased.The ink marks can be wiped easily and cleanly without any trace,and water-based and oil-based contaminants can easily slip from the surface of coatings without leaving marks at a tilt angle of 30°.(4)PU-g-PDMS2.0 coating was prepared on the tinplate,then it was dipped into NaCl solution(1.0wt.%)to observe the rust phenomenon compared with uncoated tinplate.There was obvious rust on the surface of the uncoated tinplate,and it became worst with time going.However,without corrosion was found on the surface of the tinplate with PU functional coatings.(5)Degradation property of PU-g-PDMS2.0 coating was investigated in NaOH solution(1.0wt.%).With the degradation time increasing,weight loss of the coatings increased.Morphology of coating observed by SEM illustrates that damage and cracks of coating became more obvious sereral days after.