M.Sc Thesis

M.Sc StudentBarsht Iris
SubjectChitosan Based Hybrids as Antibacterial Additives for
the Plastic Industry
DepartmentDepartment of Chemical Engineering
Supervisor PROF. Havazelet Bianco-Peled
Full Thesis textFull thesis text - English Version


Traditional food packaging materials are used to provide only barrier and protective functions. However, various kinds of active substances can now be incorporated into the packaging material in order to improve its functionality. Such active packaging technologies are designed to extend the shelf life of food products while maintaining their nutritional quality.

Low density polyethylene (LDPE) is the most common material used in packaging. Compounding LDPE with antibacterial additives can lead to the creation of active packaging. An antibacterial additive that could be considered for this purpose is chitosan. Chitosan is a cationic polysaccharide produced by N-deacetylation of chitin from crab and shrimp shells. Its antimicrobial activity, biocompatibility and non-toxicity lead to a variety of applications. However, its hydrophilic character is incompatible with the hydrophobic LDPE. The mechanism of its antimicrobial activity is still unknown but it is most likely due to the presence of amine groups.

In this research we aimed to develop grafted chitosan which could be compatible with plastic materials. We hypothesized that chitosan grafted with acrylic acid (AA), compounded with ethylene-acrylic acid copolymer (EAA) and LDPE, could result in a more uniform distribution of chitosan in the LDPE film. The synthesis was developed in our laboratory and consisted of three steps. The first step is thiolation of chitosan, by reacting with 2- iminothiolane. 2- iminothiolane reacts with the amine group  of the chitosan but since it also has an amine group the antimicrobial activity is not harmed. The second step includes Michael type addition of the thiol to the acrylate end group in ethylene glycol dimethacrylate, ending with the chitosan macromer. The final step is polymerization of the chitosan macromer with acrylic acid, resulting in a chitosan backbone grafted with poly acrylic acid side chains.

Characterization of the final product was performed using various methods such as FTIR-ATR, TGA and DSC. FTIR-ATR results confirmed the presence of acrylic acid in the final product and the thermal analysis has shown that chitosan is appropriate to be used as an additive for packaging since it is stable at the manufacturing temperatures. Grafted chitosan has shown improved distribution in comparison to native chitosan.  Mechanical properties and antimicrobial activity of films containing the additive were examined. The films exhibited antimicrobial activity and their mechanical properties were not harmed. The option of coatings was also examined for various films (linear LLDPE and polypropylene) and fabrics and they also exhibited antimicrobial activity.