Abstract
Objective: The objective of this research is to prepare Low Molecular Weight Chitosan (LMWC) by the acid hydrolysis method, using dilute hydrochloric acid (2M). LMWC has superior properties compared to the High Molecular Weight Chitosan (HMWC), especially in terms of water solubility, antibacterial and antifungal properties. These could open new potential applications for LMWC in sectors such as the cosmetics, food, and pharmaceutical industries.
 Methods: In this work, the acid hydrolysis method was used to produce LMWC with different molecular weights starting from 500 kDa and 93% degree of deacetylations (DDA). The molecular weights of the produced grades were determined by applying Mark-Houwink equation while the %DDA was determined and verified by the use of the 1st derivative UV method and 1HNMR method, respectively. The depolymerization reactions were carried out with different time intervals to produce totally deacetylated LMWC of 30 kDa, 15 kDa, and 7.5 kDa. The LMWC was characterized by FTIR, XRD, and DSC to evaluate the functionality, microstructure and thermal properties.
 Results: The FTIR spectra revealed that there is no significant difference in the main skeletal structure of the LMWC and HMWC. On the other hand, the XRD and DSC results showed that the LMWC of different molecular weights and degrees of deacetylation are of semi-crystalline structure, similar to the HMWC.
 Conclusion: The obtained results showed that the used acid hydrolysis procedure can produce LMWC grades of desired specifications, yields, and quality which are suitable for use in different applications.
Highlights
Chitosan is a biodegradable polymer obtained from the alkaline deacetylation of chitin
Different molecular weights of fully deacetylated low molecular weight chitosan (LMWC) were prepared from high molecular weight chitosan (HMWC) (500 kDa, 90% degree of deacetylation (DDA)) using 2M hydrochloric acid (HCl)
According to the results shown in the fig. it is evident that at a constant concentration of HCl, the molecular weight of the resultant chitosan polymers decreases as the reaction time increases
Summary
Chitosan is a biodegradable polymer obtained from the alkaline deacetylation of chitin. Both chitin and chitosan are linear copolymer which consists glucosamine and N-acetyl glucosamine repeating units, linked by β (1,4) glycosidic bonds as shown in fig. The characteristics of chitosan in solutions depend on its degree of deacetylation (DDA), distribution of acetyl groups, chain length, molecular weight distribution, and solubility [4]. Chitosan has been investigated for various potential applications in the pharmaceutical industry [10,11,12], especially in designing and developing different drug delivery systems. The free amino groups attached to glucosamine monomers complexes with different anionic drugs, and could be utilized in the design of different drug delivery systems [14]
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