| The main adhesives used in label industry are polyvinyl formaldehyde,polyacrylate,modified starch and casein.The above adhesives have the problems of producing harmful gas(formaldehyde),too much water resistance making difficult to recycle bottles,poor water resistance and high price.With the gradual shortage of petroleum resources,the adhesive industry began to develop towards the direction of low-cost,green and environmentally friendly renewable adhesives.Peanut meal,which contains a high proportion of protein,is a natural and renewable functional polymer with excellent film-forming properties,and is considered as a promising alternative to petroleum-based adhesives.However,the problems of low bonding strength and poor water resistance of the adhesive prepared by peanut meal have limited its application in beer label industry.In order to solve the above problems,the research of this paper is as follows:In this paper,the label adhesives were prepared by cold-pressed peanut powder with4,4’-diphenylmethane diisocyanate(MDI)as cross-linking agent to enhance the adhesive properties(viscosity,bonding strength,water resistance duration,etc.).The best preparation technology of PM based label adhesive was determined by single factor test.The mechanism of MDI crosslinking modification and the enhancement mechanism of PM based label adhesives after modification were explored.The anticorrosion resistance of PM based label adhesives were improved by adding preservative.It provides a method and theoretical basis for the application of peanut meal protein in adhesive.First of all,the effects of the amount of crosslinking agent,solid-liquid ratio,reaction temperature and reaction time on the properties of PM based label adhesive were studied by single factor experiment,and the optimum preparation conditions of the label adhesive were as follows: the amount of crosslinking agent was 15%,the ratio of material to liquid was 1:5,the reaction temperature was 50℃,and the reaction time was 1 h.Under these conditions,the comprehensive properties of the label adhesive(viscosity: 82.22 Pa·s,bonding strength:1.14 MPa,solid content: 18.59%,Water resistance time: 77 h)was the best,applied to beer label with high bonding strength and water resistance.Secondly,different PM based label adhesive samples were prepared by adding different amounts of MDI,using the solid-liquid ratio,reaction temperature and reaction time in the optimal preparation process.The contact Angle of PM-based label adhesive on the glass surface increased with the increase of the amount of crosslinking agent.When the amount of crosslinking agent was greater than 15%,the contact angle on the glass surface was greater than 90°(indicating that the label adhesive has no wettability on the glass surface),which led to the reduction of its bonding strength.The results of Fourier transform infrared spectroscopy(FTIR)showed that MDI reacted with the active groups(hydroxyl,amino)on the surface of peanut protein molecules to form the amino ester bond and urea bond,which promoted the formation of the crosslinking structure of the adhesive system.X-ray diffraction(XRD)analysis showed that the crystallinity of PM-based label adhesives increased from 15.79% to 19.20% before and after modification,which was due to the more orderly arrangement of protein molecules in the adhesives system due to the crosslinking effect of MDI.The results of thermogravimetric analysis(TGA)showed that the highest degradation temperature of PM based label adhesive increased from 300℃ to 306℃ after curing,which indicated that the MDI-modified adhesive system had higher thermal stability.The microstructure of PM-based adhesive after curing was observed and analyzed by scanning electron microscopy(SEM),the results show that the surface structure of the MDI modified adhesive was more compact and smooth after curing,which could effectively prevent the penetration of water molecules.Therefore,the water resistance of PM based adhesives were improved.Finally,the PM based label adhesive was selected under the optimal preparation conditions,and three preservatives(sodium diacetate,calcium propionate,sodium tetraborate)were added according to the gradient,respectively.The inhibition effect of three preservatives on the growth of Aspergillus flavus and Aspergillus Niger were studied,and the types and dosage of preservatives were selected and optimized.The results show that the inhibition effect of sodium tetraborate on the growth of Aspergillus flavus and Aspergillus Niger of PM based label adhesive was the best,and when the addition amount of sodium tetraborate was 0.75%,the number of days of inhibiting the growth of the two kinds of mold colonies was more than 10 days(indicating effective anti-corrosion properties),and the area of PM based label adhesive for the two kinds of mold infection was 0.In addition,the addition of sodium tetraborate has no significant effect on the water resistance of PM based label adhesive. |
