Valorisation of coffee waste for cellulose extraction using alkali and bleaching treatments

Abstract

Coffee is the second most traded commodity worldwide, playing an essential role in international economies and diverse consumer cultures. Coffee consumption is constantly increasing, which leads to large amounts of organic waste, especially spent coffee grounds (SCG). SCG are the primary waste associated with the coffee industry, and therefore valorisation of SCG can reduce the amount of waste globally and promote sustainability.

Cellulose is one of the main components of SCG and a renewable resource. It is widely valued for its biodegradability, renewability and versatile applications. Cellulose-derived biopolymers can replace oil-based plastics and be utilized across various industries. Extracting cellulose from SCG offers a potential alternative for producing pure cellulose for a variety of applications, facilitating environmentally friendly material development.

This thesis consists of a literature review and an experimental part. First, it presents the principles of cellulose, its applications and the results of previous studies on cellulose extraction with the same methods. Additionally, it addresses SCG, focusing on their composition and the motivation behind their utilization. The goal of the experimental part was to extract pure cellulose from SCG using methods and conditions based on a previous study. The experimental part examines the extraction of cellulose from ethanol pretreated SCG using sodium hydroxide (NaOH) alkaline treatment, followed by hydrogen peroxide (H2O2) bleaching.

Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis were conducted to determine the chemical composition and structure of the extracted cellulose, with microcrystalline cellulose (MCC) as a reference sample. The FTIR spectra of the extracted cellulose exhibits functional groups typical of cellulose, indicating that the chemical treatments successfully extract pure cellulose. XRD analysis shows that the extracted cellulose exhibits characteristic crystalline and amorphous regions typical of cellulose; however, the treatments had effects on its crystalline structure. Samples taken from various phases of the extraction process were examined using scanning electron microscopy (SEM), and it was observed that the sample surface changes from smooth to rough as the extraction process progresses, as chemical treatments removes non-cellulosic components from SCG.

This thesis supports previous literature, emphasizing the efficiency of the extraction methods and conditions used for successful cellulose extraction. Utilizing SCG as a source of cellulose promotes the sustainable use of renewable natural resources and contributes to development of circular economy and sustainable material development.