Feasibility of lignocellulose as feedstock for biological production of super absorbent polymers

Abstract: Super absorbent polymers (SAP) can absorb liquid many times its own weight and is used in diapers and incontinence pads. The most common type of SAP is cross-linked polyacrylic acid. The production of acrylic acid uses crude oil as starting material. This means that the final price of acrylic acid is affected by the price of crude oil which is expected to rise. This has led to an increasing interest in developing a sustainable bioproduction process that uses renewable lignocellulosic raw material for the making of acrylic acid. Lignocellulose is the material that plants and trees consist of and it contains big amounts of sugar. Sugar molecules in lignocellulose can serve as substrate for microorganisms that can transform them into 3-hydroxipropionic acid, which in turn can be converted to acrylic acid. In order to use the sugar molecules from lignocellulose, some type of pretreatment is required. However, the pretreatments that are available today are not efficient enough to be applied on a large scale and some also cause the formation of microbial inhibitors. The microbial conversion of sugar to 3-hydroxipropionic acid do not show sufficient efficacy so far, but the process is under development and improvements are regularly made. Furthermore would it be advantageous if polymerization of acrylic acid could be made directly in the fermentation broth without any energy consuming separation stepsAttempts to polymerize acrylic acid in fermentations broths from yeast have been performed. The SAP properties; absorption capacity, absorption capacity under pressure and gel strength were evaluated by methods commonly used in the hygiene industry. These characteristics are important if the SAP is to be used in diapers and incontinence pads. To examine what compounds in the fermentations broth that affected the polymerization process and SAP properties, an experimental design was made. With help of the design quantitative and statistical methods were used to determine which compound had an impact. Four groups of compounds were selected for examination; sugars, alcohols, acids and aromatic compounds. The results of the experiments conducted showed that it is possible to polymerize SAP in fermentation broth from yeast using acid pretreated spruce as sugar source. The characterization showed that the absorption capacity was unchanged while the gel strength deteriorated significantly. It was also noted that SAP polymerized in fermentations broths had strong colors in contrast to conventional SAP, which is white. Qualitative and statistical analysis showed that the aromatic compounds affected the polymerization and SAP properties negative.