Preparation And Properties Of Crosslinked Deacetylated Konjac Glucomannan Based Composite Films

With the emphasis on environment and health,in order to reduce the environmental pollution caused by petroleum based plastics,the development of biodegradable natural polymer packaging film has attracted great attention.Konjac glucomannan（KGM）is a natural water-soluble polymer with good film-forming property,biodegradability,safety,rich resources and low cost.As an edible packaging film,KGM has many hydrophilic groups and poor strength and hydrophobicity,which limits the wide application of KGM film.KGM can improve its hydrophilicity and produce synergistic effect by compounding with other polysaccharides and deacetylation,which can make up for the shortcomings of single substrate films.Deacetylated konjac glucomannan（DKGM）can be obtained by removing acetyl group in alkaline condition.Pectin or carboxymethyl chitosan forms crosslinking structure with calcium ion.The two crosslinking modification are carried out simultaneously to prepare composite film with excellent comprehensive performance.In this paper,KGM,pectin and carboxymethyl chitosan were used as raw materials,and then calcium hydroxide suspension was used to modify the composite films to explore the changes of structure and properties of the composite films.The main research contents are as follows:（1）Firstly,low ester pectin was prepared by alkali deasterification,and then DKGM/Ca-PEC composite films with different proportions were prepared by soaking Ca（OH）₂ suspension with KGM and low ester pectin as basic materials.Infrared spectroscopy confirmed that low ester pectin was successfully synthesized,KGM in composite film had achieved deacetylation,and pectin had cross-linked with calcium ion.The mechanical property test showed that DKGM/Ca-PEC composite films have smaller thickness and higher tensile strength,it reaches the maximum value of 48.1MPa when pectin content 40%.Hydrophilicity test showed that when pectin accounted for 40%,the swelling degree and water solubility of DKGM/Ca-PEC composite films were the lowest,which were 60.54%and 19.43%respectively,and the water vapor permeability was only 2.76×10^-7 g·（m·d·Pa）^-1。Deacetylation of KGM and crosslinking of pectin can enhance the intermolecular force and make the molecular chain entangled more closely,significantly improve the strength,barrier of the composite film and effectively reduce the hydrophilicity.When the PEC content 40%,the comprehensive performance is the best.In the strawberry preservation experiment,the changes of color and hardness of strawberry packaged with DKGM/Ca-PEC40 composite film were slower than those of the blank group.The mass loss was more than 10%after 7 days,which effectively prolonged the storage period of strawberry for about 3 days.（2）KGM/CMCS composite films and DKGM/Ca-CMCS composite films were prepared by using carboxymethyl chitosan（CMCS）with bacteriostasis and KGM as material,adding calcium hydroxide suspension.After adding Ca（OH）₂,the film-forming solution will turn milky white.Combined with infrared spectroscopy,it is judged that the deacetylation of KGM and the crosslinking of CMCS were realized at the same time.SEM images showed that the surface of the composite films were smooth and had good compatibility.The addition of CMCS can improve the elongation at break of the composite film,deacetylation and crosslinking can also improve the mechanical strength of the composite film.When CMCS accounts for 50%,the barrier property of DKGM/Ca-CMCS composite film is the best,and the water vapor permeability is 1.83×10^-7 g·（m·d·Pa）^-1,which is about 10%of the film before modification,and the swelling degree and water solubility are the lowest,74.73%and10.76%respectively.When CMCS content 50%,the comprehensive performance of DKGM/Ca-CMCS composite film is the best.The strawberry preservation test showed that DKGM/Ca-CMCS50 composite film could promote the preservation of fruits and vegetables.The weight loss rate of the coated strawberries was less than 5%on the fifth day,which had full commercial value.After seven days,the weight loss rate was only 8.89%,which prolonged the storage period of strawberries by 4-5 days.