Development of Renewable and Sustainable Chitin based Nanomaterials

Abstract

A million tonnes of waste from crab, shrimp, and lobster are generated throughout the world. Without proper treatment, they can cause environmental problems when they are discarded, or waste treatment is quite expensive (US$150) per tonne. Nonetheless, with the development of technology and more concerns about the environment from governments and citizens, the waste can be redefined as a biomass resource. These wastes contain calcium carbonate (20-50%), chitin (15-40%), and protein (20-40%), having extensive application in diverse industrial fields from pharmaceutical, agricultural, medical to plastic. Besides, recently, biomass-based plastic has drawn a lot of attraction among research communities due to its renewable resource, biodegradability, and some unique properties compared to traditional petroleum-based plastic. In this thesis, from crab/shrimp water, chitin nanomaterials are extracted and synthesized, showing potential application and high performance to solve current problems. The first part of my thesis is to synthesis nitrogen (N)‐doped chiral carbon nanomaterials. The conventional hard‐template methods for nitrogen (N)‐doped chiral carbon nanomaterials require complicated construction and removal of the template, high‐temperature pyrolysis, harsh chemical treatments, and additional N‐doping processes. If naturally occurring chiral nematic chitin nanostructures [(C8H13NO5)n] in exoskeletons were wholly transformed into an N‐doped carbon, this would be an efficient and sustainable method to obtain a useful chiral nanomaterial. Here, a simple, sacrificial‐template‐free, and the environmentally mild method was developed to produce an N‐doped chiral nematic carbon‐sheath nanofibril hydrogel with a surface area >300 m2 g-1 and enantioselective properties from renewable chitin biomass. Calcium‐saturated methanol physically exfoliated bulk chitin and produced a chiral nematic nanofibril hydrogel. Hydrothermal treatment of the chiral chitin hydrogel at 190 °C created an N‐doped chiral carbon‐sheath nanofibril hydrogel without N‐doping. This material preferentially adsorbed D‐lactic acid over L‐lactic acid and produced 16.3 % enantiomeric excess of L‐lactic acid from a racemic mixture. In the second part of my thesis, I will show the fabrication of a high gas barrier coating layer from nanocellulose/nanochitin onto a commodity plastic - polypropylene. Currently, polypropylene is widely used as food packaging material owing to its low price, ease of the process, high strength, clarity, and high water vapor barrier property. However, its low oxygen gas barrier limited its usage to several food products. Specific barrier solutions are employed for conventional polymer films to increase the gas barrier property and extend shelf-life of the packaged food product. Low oxygen and water permeability are critical values for food packaging material, which preserves the quality of food products. Secondary importance to barrier property, which makes a type of packaging suitable for a specific purpose, is its toxicological properties. The critical requirement for food packaging material is non-toxicity that should meet some legal guidelines from the government. Herein, in this research, we employ the aqueous solution of cellulose nanofibril (CNF) with negative carboxyl charges and chitin nanowhisker (ChNW) with positive amine charges to add a multilayer coating layer with high water vapor/oxygen barrier property onto polypropylene through layer-by-layer (LbL) assembly technique. Our coated material has a low oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) values that meet the requirements of food packaging materials for most of the targeted food products. The coating layer is not only transparent but also shows a less detrimental effect on the environment when the film is subjected to incineration. The final material shows potential as a viable option in food packaging market.