交聯化反應對幾丁聚醣-三聚磷酸鈉薄膜物性之影響

Abstract

幾丁聚醣(chitosan)薄膜具生物可分解、生物相容性高、安全無毒等優點，已被廣泛運用於各領域，然而其防水性、機械性等性質仍有許多改進空間。幾丁聚醣是葡萄糖胺單體和乙醯葡萄糖胺單體經由 beta-1,4 糖苷鍵組成的共聚合物，可由幾丁質(chitin)經去乙醯化製備而成，其在酸性溶液中是帶正電的聚合物(pKa = 6.5)，能和帶負電離子透過靜電引力形成物理性交聯。本研究選用三聚磷酸鈉 (sodium tripolyphosphate)為交聯劑，旨在改善薄膜防水性和機械性，以增強在包裝材料上的應用性。薄膜交聯度以茚三酮試驗(ninhydrin assay)檢測，並佐以傅立葉紅外線光譜，探討交聯度和水溶性、水氣透過率、機械性質、表面形態等物性之關係。經三聚磷酸鈉交聯的幾丁聚醣薄膜，於酸性環境(pH=1.9)水溶性大幅下降至15.68%，抗張強度顯著提升，由 64.5 Mpa 上升至 146.5 MPa，與茚三酮測得之交聯度呈現正相關。研究發現，幾丁聚醣薄膜的抗張強度能藉由交聯化反應改善，且酸性環境下溶解度隨交聯度提升呈現下降趨勢。

Chitosan is a biodegradable, inexpensive, biocompatible and non-toxic polysaccharide with good film-forming properties. It is a copolymer of glucosamine and N-acetyl glucosamine linked by beta 1,4-glucosidic bonds obtained by N-deacetylation of chitin. Chitosan films were applied in drug delivery systems, reverse osmosis and filtration, ect. However, the application in food packaging industry was restricted due to some disadvantages such as higher water swelling ratio and poor water-shielding ability. Cross-linking, as a result, is applied in order to overcome these problems. Since chitosan is a polycationic polysaccharide in acidic medium (pKa 6.5), it forms gels with the gentle and nontoxic multivalent counterions, tripolyphosphate (TPP), by electrostatic forces. However, few studies have been conducted to investigate the relationship between the degree of cross-linking and mechanical properties, water vapor transmission and solubility of chitosan-tripolyphosphate films. In this study, the effect of degree of cross-linking was determined by ninhydrin assay and the cross-linked films were characterized with regard to mechanical properties, solubility in water, water vapor permeability and IR spectroscopy. The solubility of chitosan films was reduced to 15.68% in acidic (pH= 1.9) solution by cross-linking, which is inversely proportional to degree of cross-linking of chitosan films. Tensile strength was increased from 64.5 Mpa to 146.5 MPa, directly proportional to degree of cross-linking of chitosan films. Results indicated the hydrophobicity in acidic solution and mechanical properties can be improved by cross-linking, and the degree of cross-linking can be measured by ninhydrin assay.