Preparation and properties of bio-geopolymer composites with waste cotton stalk materials

To promote the effective utilization of plant stalk resources, cotton fibers and cotton powders were obtained by crushing and screening waste cotton stalks, which were then utilized for the preparation of bio-geopolymers. This study explores the influence of the size and content of cotton stalk fibers and curing methods based on the physical and mechanical properties of a geopolymer. Pretreatment of cotton stalk was applied to improve the fiber-matrix bonding performance and enhance the mechanical properties of the proposed geopolymers. Compressive and flexural bending tests and a hydrochloric acid erosion test were carried out to measure and evaluate the bio-geopolymers containing cotton stalk powder. Scanning electron microscopy and X-ray energy spectrometer (SEM-EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) techniques were applied to investigate the micro-characteristics of the geopolymerization products. The test results demonstrate that the addition of untreated cotton stalk fibers reduces the density of the geopolymers and the compressive strength, whereas the flexural strength is slightly increased. Alkali treatment has proven to be effective in fiber-matrix bonding, and the compressive and flexural strengths are improved by 4.8% and 11.5% respectively compared to the untreated ones. The cotton stalk powder can effectively improve the compressive strength of geopolymer, while the acid corrosion resistance of bio-geopolymer decreases. Through SEM-EDS, XRD, and FTIR analyses, the effects of cotton stalk powders on geopolymer are mainly filling and cementing. The sugar precipitated from cotton stalk in alkaline environment reduces the compactness of a geopolymer gel. Alkali treatment and PVA solution treatment on cotton stalk can effectively reduce the effect of the precipitated sugar on geopolymer gel.