Study And Preparation Of Biodegradable Coating Used For Straw Tableware

Increasingly environmental problems are emerged in for the mass application of nondegradable plastics,which urges the research on degradable alternatives.The straw or stalk derived of crops is abundant and biodegradable;its utilization is an effective strategy to alleviate the serious environmental problems.But now,massive straw or stalk is disposed of by being burned for fertilizer,which cause much more serious air pollution.In order to reduce the huge environmental pressure brought by burning straw and stalk,we prepared disposable tableware with straw and stalk in place of traditional plastics.However,there are still some problems in the straw or stalk utilization.The crucial problem to be solved is water resistance for the straw products.Herein,we designed a coating composite which has been applied for straw tableware substrate.The coating composite is precipitate to pocess both water-resistant and biodegradable properties.In this investigation,corn starch was first esterified and then was modified by coupling agent,and then,the as prepared modified starch was mixed with an acrylic emulsion,forming a composite coating.The molecular structure,particle morphology,crystal structure and thermal properties of modified starch were analyzed by FTIR,¹H NMR,XRD,SEM,DSC and TG,respectively.FTIR and Mapping analysis confirmed desirable groups combined with the starch molecular,and the modified starch was successfully prepared by microwave dry method.After modification,the crystalline structure of EST starch was not changed,but the morphorlogy was damaged（the grains were broken and became more coarse）.DSC result indicated that the Tg of modified starch was increased after esterilization,and thermogravimetry（TG）analysis displayed poor thermal stability due to the damage of the grain morphology.Furhtermore,we explored several influencing facors,such as microwave power,reaction time,estrifying agent and coupling agent,on esterification degree,and thereof the water-resistance of the esterified starch.The results indicated that with increase of time,the DS of starch sterate increased first and then decreases;with increase of power,the DS increases;with increase of stearic acid or H₂O content,the DS of starch sterate incresased first and then decreases.On this basis,the suitable reaction conditions of KH-570 surface modified EST starch were as follows:reaction time 4h,reaction temperature 70℃,k H-570:H2O:CH3CH2OH ratio 5:4:20 or 5:6:20（KH-EST-1 or KH-EST-2）.In order to increase the content of starch in emulsion,EST starch mixed emulsion was studied on water resistance.The results showed that the higher the substitution degree of EST starch,the better the water resistance of the mixed emulsion,and the substitution degree of EST starch was 0.01006.The higher the content of EST starch in the mixed emulsion,the worse the water resistance,and the water resistance of EST starch and acrylate emulsion is 1:4 is better.KH-EST starch has better water resistance than EST starch,and the ratio of starch to acrylate emulsion is 1:4.The weight loss rate of starch/acrylate 1:4 mixed emulsion coating was 12.96%in 30 days and 20.53%in 120 days.The starch was basically completely degraded.