Preparation And Properties Of High Strength And Flame Retardant Pea Starch/Polyvinyl Alcohol Composite Aerogel

Natural starch is abundant in resources,green,renewable,biocompatible and biodegradable and has received much attention as the matrix of aerogels.However,traditional starch aerogels are weak and flammable,limiting their wide application.In this thesis,to meet the practical application better,starch-based aerogels with good mechanical properties and flame-retardant property were prepared by lyophilization technology utilized pea starch as the matrix.Firstly,the effect of the solids content on the mechanical properties of pure pea starch hydrogel was determined.The results showed that gelation did not occur when the solids content was lower than 5.5 wt%.Above 5.5 wt%,the gel strength increased with increasing the solids content.However,when the solids content reached 8 wt%,much starch solution remained and gelled in the gelatinization container,resulting in less gel.Therefore,taking the economic benefit and other factors into comprehensive consideration,the final solids content of pea starch was selected as 7.5 wt%.Then,flexible polyvinyl alcohol(PVA)was added and composite pea starch/PVA hydrogels were obtained,in which borate was further introduced as covalent crosslinks to achieve starch-based aerogel with good flame retardancy.The flame retardancy and thermal stability of the obtained aerogels were investigated by limiting oxygen index measurement,micro-calorimetric test and thermogravimetric analysis.The results showed that the limiting oxygen index(LOI),total heat release(THR)and residual carbon ratio of pea starch/PVA composite aerogel without borate introduction were18.8%,14.5 k J/g and 12.46% respectively,while the composite aerogel obtained after treating the corresponding hydrogel with borax solution achieved an LOI of more than33.0%,a THR of 4.8 k J/g and a carbon residue ratio of more than 45%,indicating that the flame retarding property of the composite aerogel could be greatly improved after borax treatment.Finally,chitin nano-whisker(CNW)with crystallinity of 81.48%,average length of 400 nm,width of 20 nm and aspect ratio of 20 was prepared by acid-hydrolysis method.The obtained CNW was introduced into pea starch/PVA composite aerogel.The effect of CNW on the flame retardancy and mechanical properties of pea starch/PVA composite aerogel was investigated.It was found the LOI of the composite aerogel with CNW addition and borax solution treatment exceeded 35.0%,the THR was reduced to 4.4 k J/g and the residual carbon ratio was higher than 48%,indicating that addition of boron and nitrogen elements had a synergic effect on the improvement of the flame-retardant property of pea starch/PVA composite aerogel.