Wood-derived Biopolymers for Photonics

Abstract

Currently, conventional plastics and composites that we mostly use are derived from petroleum which is a non-renewable resource. Plenty of these plastics are designed for a single purpose such as water bottles and food packaging and end up in landfills, causing significant environmental impact since the degradation rate is extremely slow and can take centuries. The unstable market of petroleum and its contribution to global warming are other concerns associated with conventional plastics. On the other hand, plant-based natural polymers or biopolymers are sustainable, yearly renewable, and environment-friendly solution to the current problem associated with conventional plastics. Biodegradable polymers such as cellulose and lignin can be obtained from plants and have applications in various fields e.g. construction, agriculture, fuel, etc. Initially in this work, wood-derived cellulose nanocrystals (CNCs) are utilized as a matrix material to guide light in the luminescent solar concentrator. Acrylic polymer emulsion, otherwise known as PMMA, is the most commonly used polymer for such purposes. Though this polymer is biocompatible, it is not biodegradable. The recycling of acrylic polymer is also complicated and if not properly done it might release harmful fume during combustion. Here waveguides made of acrylic polymers and cellulose are fabricated with organic dyes and it is found that cellulose has the potential to be used as matrix material. Easy recyclability of a cellulose-made waveguide is another factor that is investigated, and no significant performance drop is reported when waveguided made of recycled cellulose is characterized. Afterward, CNCs and lignin, another wood-derived polymer, have been investigated for their suitability to be used as radiative cooling material. Different structures have been proposed over the last few years for radiative cooling but most of these structures are not realistic for mass production due to associated cost and complex fabrication process. In these works, two structures made of cellulose and lignin are found to have a cooling temperature of 3.97 °C and 3.7 °C below ambient temperature respectively, with significant cooling power. Attaching these polymer structures on the solar cells has shown a performance enhancement by lowering the operating temperature of the solar cell. By offering a very simple and low-cost fabrication process as well as compatibility with large-scale production using an earth-abundant material, these developed structures provide an excellent opportunity to mass implement biopolymers. In the end, the scattering property of CNCs is leveraged to show their potential for enhancing the light quality of light-emitting diode (LED). White LED is the most common one and can be conveniently fabricated using phosphor and blue LED chip. It is demonstrated that CNCs can scatter the blue light effectively which would increase blue to yellow light conversion and improve the uniformity of correlated color temperature. The proposed structure for white LED has shown better light quality and ~30% enhancement in luminous flux compared to a conventional LED structure without using CNCs. Overall, this thesis work focuses on different aspects of biopolymer properties and shows their potential application in different fields of photonics.