Ph.D Thesis

Ph.D StudentBar Hedva
SubjectA New Approach for Tailoring the Properties of Shellac
DepartmentDepartment of Biotechnology
Supervisor PROF. Havazelet Bianco-Peled
Full Thesis textFull thesis text - English Version


Shellac is a unique natural resin comprising a mixture of polyesters and single esters, which is refined from the secretion of insects in south Asia. It is widely used as a preservative coating or a confectionary glaze in the food industry and as an enteric coating in the pharmaceutical industry. Remarkably, the physico-chemical characteristics of shellac, in particular its excellent film forming, low vapor permeability and good adhesion properties, are very untypical to low molecular weight materials. Yet, the molecular architecture and morphology of the film were not investigated. Furthermore, despite the high potential of shellac as an environmentally friendly protective coating, its utilization is still limited due to its mechanical brittleness and poor stability caused by self-polymerization reactions. The study was aimed at gaining insights into the structure-property relations in shellac and exploring a new strategy that will reduce the drawbacks of shellac and enhance its stability. Small angle x-ray scattering and high resolution electron microscopy experiments revealed a unique bicontinuous nanostructure in shellac. Using manipulations of shellac’s composition and studies of shellac solutions in ethanol, we could identify the hydrophilic phase, the lipophilic phase, and the amphiphile residing on the interface between them. The bicontinuous morphology, typified by an extremely large interfacial area, was used to explain shellac’s physicochemical characteristics and mechanical properties. Compounding shellac with the biocompatible modifying agents Jeffamine? has led to superior mechanical properties of the film compared to native shellac as well as preservation of the physical and mechanical properties upon aging. Based on Fourier Transform Infrared experiments, these beneficial effects were attributed to formation of amide bonds and acid-base interactions between shellac and Jeffamine?. Hence, the Jeffamine? modification succeeds in hindering self-polymerization occurring in native shellac and provides a significant improvement in the stability and shelf-life of shellac coating. Understanding the exceptional morphology of shellac along with enhancing its stability and shelf life may open the way for better control over shellac’s properties and its utilization for novel applications in drug or pesticide delivery systems.