Study On The Construction And Properties Of Network Of Corn Starch-based Hydrogel

As a natural biomacromolecule,starch has excellent characteristics of being economical,biodegradable,and renewable for applications,which has attracted widespread interest in the field of food processing,biomedicine,agricultural production,and material science.The use of starch to prepare polymer composites with special functions can promote the high-value utilization of starch resources.This study aimed to solve the problems of poor mechanical strength,insufficient toughness,and limited application range of starch hydrogels caused by weak molecular chain interactions and uneven network of starch hydrogels.Thus,a series of high-strength and high-toughness starch-based hydrogels were constructed by combining dual-network crosslinking technology,nanocomposite technology,in-situ self-assembly technology,coating technology,etc.These physical and chemical methods have reinforced the cross-linking network structure of starch hydrogel and endowed them with the biological activity,which provide a reference for strengthening the mechanical properties of starch hydrogel and expanding its application range.The main results are shown as follows:(1)Aimed to strengthen the starch gel strength,this study constructed a starch/PVA/borax dual cross-linked(DC)hydrogel with high stretchability,self-recovery,and self-healing capability based on the hydrogen bonds and boronic ester bonds.Compared with conventional starch hydrogels,the as-prepared DC hydrogels exhibited a remarkable extensibility(ca.2485%),excellent toughness(ca.290.5 k J·m^-3),high compression strength(ca.547.8 k Pa)and rapid self-recoverability(81.9%of energy recovery after resting for 30 min).More importantly,the DC hydrogel can sustain a loading weight of 1000 g(approximately 300 times of its own weight)for more than 5 min.Upon removal of the load,the DC hydrogel rapidly recovered its original shape within 15 s and exhibited a rapidly effective self-recovery.Furthermore,the hydrogel also exhibited an outstanding self-healing capability at room temperature both in air and underwater.Especially,the elongation at break of the healed hydrogel can still reach 20times of its own length.(2)Introducing nano self-assembly technology to strengthen the network nodes and then further improve the mechanical strength of the hydrogel,we successfully prepared a mechanically stiff,fatigue-resistant,and excellently adhesive microspheres-strengthened debranched starch/polyvinyl alcohol double network hydrogels(W-Gels).The debranched starch can in-situ self-assemble into 3D waxberry-like microspheres particles composing of nanoparticles,which acted as gel network nodes and embedded in the double network to strengthen the network skeleton structure.The compressive strength of W-Gels reached up to780.7±27.8 k Pa,and the gel can sustain about 2000 times of its own weight.It was found that the recovery efficiency exceeded 93%after the 60th compressive successive loading-unloading cycle under 50%strain.Moreover,the hydrogel can adhere onto soft or hard substrates,such as skins,plastics,gauzes,glasses,and metals.Simultaneously,the gel strip firmly attached to the author's fingers without any external force could be stretched to more than 8 times its original length.(3)Based on the structure of starch chain network and 3D microspheres in gel network skeleton,we adopted the annealing treatment technology to rearrange the starch molecular chains of hydrogel and then strengthen the mechanical properties of the gel network,finally obtained a reinforced hydrogel with a rearrangement network structure.Notably,the tightly arranged network structure realized the transformation of the compressive stress of starch-based hydrogel from k Pa level to MPa level.Compared with the unannealed W-Gel₄,the compressive stress and tensile stress of the W-Gel₄ after annealing treatment for 24 h(W₄-A₂₄)were reached up to 1.981 MPa and 663.8 k Pa,increased by 2.54 times and 4.72 times,respectively.Especially,compared with waxy corn(15.4 k Pa)and corn starch(34.7 k Pa)hydrogels,the compressive stress of W₄-A₂₄ was increased by 128.64 times and 57.09 times,respectively.The lamella structure of was thicker and a layer-by-layer arrangement with the 3D microspheres in the annealed hydrogel was observed by SEM.(4)Given that the ion induced the rearrangement of PVA chains in the network and improved the compactness of the gel network structure,the high hydration power of sulfate ion and sulphate ions was used to construct a starch-based hydrogel with high strength and toughness by breaking the steady state of the hydrogen bond between the PVA molecular chain and water molecule,and promoting the crosslink of PVA molecular chain to form a denser PVA gel network.Simultaneously,the 3D microspheres would further rearrange by the PVA network shrinks.After ion treatment,the network structure of W-Gel₄ changed from a random stacking arrangement to an ordered structure which 3D microspheres were embedded and filled into the honeycomb gel network,as well as the pore walls of the gel network are thicker and denser.At the same time,the moisture content of the gel significantly reduced to below 80%.Moreover,the mechanical strength of hydrogel has increased markedly,the compressive stress and tensile stress of starch-based hydrogels have reached the goal of MPa-level strength.After ion treatment,the compressive stresses of W-Gel₄-S6 and W-Gel₄-P6 were reached up to 3.791MPa and 3.094 MPa,the tensile stresses were 1.37 MPa and 1.27 MPa,as well as the elongation at break were 668.3%and 807.3%,respectively.Among them,the compressive stresses of W-Gel₄-P6 and W-Gel₄-S6 enhanced 200.91-246.17 times and 89.16-109.25 times higher than the waxy and normal corn starch gel,respectively.(5)Combined with coating technology,we further reinforced the mechanical properties of starch-based hydrogels.Due to the coordination reaction between the phenolic hydroxyl organic ligand(TA)and Fe^III,the coating film was introduced into the ion-enhanced hydrogels(W-Gel₄-S6 and W-Gel₄-P6)by the adhesion characteristic of the metal-phenolic network(MPN)to construct a novel and functionally-modified hydrogel(MPN@W-Gel₄-S6 and MPN@W-Gel₄-P6).The results showed that MPN effectively increased the mechanical properties of the hydrogel.When the compressive strain is 90%,the compressive stresses of MPN@W-Gel₄-S6 and MPN@W-Gel₄-P6 were 4.16±0.33 MPa and 3.48±0.15 MPa,and the elongation at break increased to 716.2%and 921.4%,respectively.Furthermore,based on unique nature of TA,the functionalized surface modification strategy provided the starch hydrogel with excellent inhibiting effects against Escherichia coli and Staphylococcus aureus In-vitro cell and degradation assays confirmed that MPN@W-Gel₄-S6 and MPN@W-Gel₄-P6exhibited low-cytotoxicity,high biocompatibility,and biodegradability.