Starch Enhances The Preparation And Performance Of Highly Self-healing Polyacrylic Acid Hydrogels

As a renewable natural polymer material,starch has outstanding features of being ecofriendly and economical for applications,which has attracted widespread interest in the field of material science.The use of starch to prepare polymer composites with multi-functions can take greater advantage of starch resources,which is of significance.In this study,starch was introduced into polymer gel networks,which not only effectively improved the mechanical properties of the composite hydrogel,but also endowed the hydrogel with excellent self-healing properties upon damage.Acrylic acid was used in this work as the main bulk material,starch was added as a reinforcing component,and starch-acrylic composite hydrogels were prepared through graft polymerization,free radical polymerization,etc.Results show that the obtained hydrogels have good mechanical properties and excellent self-repair functionalities.The research has created a new technical approach for the application of starch-based hydrogel materials.The work in this thesis is summarized as follows:1.In this work,the obtained hydrogels used ammonium persulfate as the initiator,and N,N'-methylene-bis-acrylamide as the cross-linking agent,a chemical cross-linking network was formed between starch,acrylic acid(AA)and 2-acrylamido-2-methyl-1-propanesulfonic acid(AMPS).Subsequently,the obtained hydrogel was simply immersed in an ethanol solution to prepare a starch acrylic hydrogel system with high self-healing properties.This study systematically investigated the effects of the monomer ratio and crosslinker concentration on the mechanical properties and self-healing efficiency of the hydrogels.The structural features of the hydrogel were characterized by ATR infrared spectroscopy(IR)and scanning electron microscopy(SEM).The mechanical properties and self-healing properties of the hydrogel were also tested systematically.The results show that when the concentration of the crosslinker is 0.1%and the monomer ratio between AA and AMPS is 8:2,the elongation at break of the hydrogel sample is more than ten times of its original length and the self-healing efficiency over 24 hours is as high as 96%;The gel system is conductive to some extent.Infrared spectroscopy(IR)results indicated that the starch was successfully introduced into the acrylic-based hydrogel system.Scanning electron microscope(SEM)results showed that the hydrogel system had a porous structure.2.The mechanism of self-healing behaviors was systematically studied.Rheometer was used to track and monitor the influence of the cross-linking agent on the gel formation process.The change of the storage modulus with time was fitted by the Hill equation,the R~2 is above99%.The experimental results show that the amount of cross-linking agent in the hydrogel can only affect its storage modulus,and no other significant effects have been observed for the cross-linking agent on the gel properties.And then,the effects of the starch usage,starch gelatinization process and the procedure of gel treatment in ethanol solution on the properties of the as-prepared hydrogel were discussed.The results show that adding starch in the hydrogel,gelatinization of the starch and ethanol soaking treatment of the raw hydrogel can all play important roles in the self-healing features of the hydrogel.The gel was also subjected to cyclic compression tests,and the results show that there are a large amount of dynamic physical interactions inside the gel.Thus,it can be reasonably argued that the excellent self-healing property of the hydrogel mainly results from the existence of a large number of hydrogen bonds and other physical interactions such as chain entanglements inside the system.3.Conductive hydrogels based on starch and AA were prepared with ammonium persulfate as the initiator and ferric chloride as the crosslinking agent.The effects of the concentration of ferric chloride on the gel mechanics and electrical conductivity were explored.The fatigue resistance of the as-prepared hydrogel was characterized by a cyclic test.The experimental results showed that the increase in the amount of ferric chloride cross-linking agent would lead to an increase in gel cross-linking density and electrical conductivity.