Preparation Of Food Grade Superhydrophobic Coatings And Their Applications

In our daily life,non-Newtonian liquid foods such as milk,yogurt,honey and fruit juice have extremely high viscosity and complex fluidity,which easily adhere to the surface of the container,resulting in serious liquid food waste.The superhydrophobic coating is a promising strategy to solve the problem of liquid waste in food packaging due to its low adhesion to liquid.However,fluorine-containing substances are most commonly used to prepare superhydrophobic coatings,which are not only expensive,but also have biological toxicity and environmental pollution.In addition,the poor stability of the superhydrophobic coating seriously limits its practical application.In this paper,ethanol and ethyl acetate were used as solvents,natural attapulgite（APT）natural nanorods,stearic acid（STA）,polydimethylsiloxane（PDMS）and paraffin wax（PW）were used as raw materials,and food grade hydroxypropyl distarch phosphate（HDP）and single component silicone（SL）adhesive were further introduced as bonding layers.The food grade superhydrophobic coating with excellent comprehensive properties was prepared.The main contents are as follows:Firstly,STA was used to modify the surface of APT nanoparticles,and edible HDP primer was introduced.Then food grade HDP/STA@APT superhydrophobic coating was successfully prepared by spraying method.The effects of STA and APT concentration on wettability and morphology of coating were studied.Due to the hierarchical structure and low surface energy of the coatings assembled by APT and STA,the coatings show excellent superhydrophobic properties,with contact angle and sliding angle to water of 158.1°and 7°,respectively.This brings good self-cleaning properties and anti-liquid adhesion properties.At the same time,the coating is also suitable for a variety of commonly used food packaging materials,such as PET,PP,glass,etc.In addition,the coating showed good mechanical and ultraviolet aging stability.Specifically,after the coating is continuously impacted by water droplets in the same position,the coating still maintains a superhydrophobic state,and at the same time,the coating can withstand UV radiation for at least 60 min.In order to further improve the stability of food grade superhydrophobic coating,APT nanoparticles were modified by PDMS,and then PW was used to further modify APT nanoparticles.Finally,edible SL primer was introduced to prepare stable SL/PW@PDMS@APT superhydrophobic coating.The effects of the concentration of PDMS@APT,ultrasonication time and the ratio of substrate to surface on the superhydrophobicity and surface morphology of the coating were systematically studied.After system optimization,the coating has:i)excellent superhydrophobicity and superthermophobic liquid property.The contact Angle and rolling Angle of the coating to water are 163.8°and 6°respectively,and the rolling Angle of the coating to hot droplets at～45°C is less than 12°;ii)excellent mechanical stability.The coating maintains its superhydrophobicity after being washed by 20 k Pa water for 20 min,bent for 1000 cycles and rubbed 9 times by A4 paper,respectively;iii)excellent chemical stability,the coating remained superhydrophobic after soaking in 1 M HCl_（aq）,1 M Na OH_（aq）and 1 M Na Cl_（aq）for 24 h;iv)excellent longer-term resistance to high viscosity liquid adhesion,no surface adhesion after 10 days of contact with yogurt coating.This paper provides a new idea for the preparation of safe,non-toxic and environmentally friendly food grade superhydrophobic coatings and the method is simple,efficient and low-cost.The two food-grade superhydrophobic coatings exhibit tremendous potential in food industry for anti-adhesion of liquid foods.