Research On The Mechanical And Adsorption Properties Of Chitosan And Its Composites

As a green and environmentally friendly marine biomaterial,Chitosan has the advantages of non-toxicity,non-pollution and easy degradation.however,chitosan is a rigid molecule with poor mechanical properties and toughness,which limits its application.As an adsorbent,chitosan contains a large number of-NH₂ and-OH groups,they can chelate with many metal ions to form complexes,which can reduce the content of heavy metals in water and achieve the purpose of purifying sewage.However,its adsorption efficiency for alkaline dyes such as methylene blue is low,which is not conducive to the wide application of chitosan in water treatment.Therefore,this paper optimizes and improves the toughness and adsorbability of chitosan,and achieves the improvement of its mechanical properties and the enlargement of its adsorption range.Firstly,the mechanical properties of chitosan membrane were improved.In order to improve the short plates with poor toughness of Cs film,PVA with better toughness was selected as toughening agent.At the same time,SA was used as auxiliary agent to improve the compatibility of PVA with Cs and to ensure better water absorption ratio of composite film.The ratio of PVA:Cs:SA=3:3:1 was controlled.In this experiment,solution blending method and coating method were used,and I prepared f _SA/PVA/Cs,f _Cs-SA/PVA and f _SA-Cs/PVAA-Cs/PVA films.The blend solution was prepared according to the ratio of PVA:Cs:SA=3:3:1,and the f _SA/PVA/Cs film was cast in a Petri dish;The pure Cs film was prepared by coating method,and then the pure Cs film was coated with SA/PVA blend solution to obtain the f _Cs-SA/PVAs-SA/PVA film;Using the same method,the pure SA membrane was prepared first,and then the pure SA membrane was coated with Cs/PVA blend solution to obtain the f _SA-Cs/PVA membrane.The results show that:Both blending and coating methods can make the PVA and Cs film matrix tightly combined,PVA can effectively improve the mechanical properties and toughness of Cs films,and the elongation at break can be increased from 22.6%to 99%.This is because PVA is a flexible chain structure.After interaction with Cs,the internal molecular chains of PVA and Cs are entangled,which makes the composite film not easy to be broken,and the toughness is enhanced.In addition,the mechanical properties and toughness of Cs films were improved slightly by blending method than by coating method.This is because in the blending process,the molecular chains of Cs and SA are entangled by PVA flexible chains,and SA plays an auxiliary role,making the molecular chains of PVA and Cs more closely entangled.However,the coating method is based on the already formed film,the effect of SA auxiliary agent is weakened,and the flexible chain of PVA is only entangled with one of the substances,and the toughening effect is limited.We also found that,in the coating method,the performance improvement of Cs/PVA coated SA is slightly better than that of SA/PVA coated Cs.This is because the entanglement between PVA and Cs molecular chains is closer than that of SA.Secondly,the adsorption properties of chitosan for alkaline dyes were optimized.In the experiment,because of the large interlayer spacing of MMT and the negative charge on the surface,I used intercalation method to compound Cs with MMT,which destroyed the crystallinity of Cs.However,Cs is insoluble in water and easy to be lost and protonated in acidic environment,and Citric acid has a strong hydrophilic group-COOH,which is also an acid group.It is easy to bind cations of basic dyes and is harmless and non-toxic.Therefore,water-soluble chitosan（CA-Cs）was obtained by acylating CA with Cs.Finally,the modified chitosan（CA-Cs）and MMT were compounded by intercalation method to prepare the final product CA-Cs/MMT adsorbent.The results show that:The adsorption capacity of Cs/MMT can reach 95 mg/g,which was four times higher than that of pure Cs.The adsorbability of Cs/MMT is improved because the compact arrangement of Cs is disturbed,the lamellar spacing of MMT becomes larger and even the lamellae are peeled off.Both structures become loose,the specific surface area increases,and the dyes are easy to enter.In addition,the combination of MMT anions with cations in alkaline dyes is beneficial to the adsorption of methylene blue.In addition,the optimum preparation conditions of CA-Cs were explored:CA:SHP=10:1,T=110^oC,CA:Cs=2.5:1,t=3 h,the yield of CA-Cs is the highest,which can be guaranteed to be over 54%.We can also learn that,the adsorption capacity of CA-Cs/MMT for methylene blue can reach 120 mg/g,which is26%higher than that of Cs/MMT and four times higher than that of Cs.This is mainly due to the introduction of-COOH groups.Finally,for the composite CA-Cs/MMT adsorbent,because of its hydroxyl group and incompletely reacted amino group,it retains the chelating ability of metal ions,the adsorbability of reactive dyes and acid dyes,and at the same time,it has the adsorbability of basic dyes such as methylene blue by modified composite.The application of this method in wastewater treatment can simultaneously treat water pollution caused by various organic dyes and metal ions,which is time-saving and efficient.