The term biopolymers may be used to describe macromolecules that are obtained from a wide variety of biological sources. In the wake of growing concerns surrounding the use of non-biodegradable synthetic polymers, they serve as ideal replacements for a wide range of engineering applications. However, given the versatility of (charged or uncharged) chemical species that form biopolymers, there are considerably large uncertainties in determining their exact chemical structure. The presence of charged species in biopolymers further complicates matters, as they remain sensitive to parameters such as acidity (pH) and ionic strength (conductivity), thereby challenging the traditional physical models that describe polymer dissolved within specific solvents.

The work presented in this thesis tries to overcome these limitations through an abstract and idealised description of their structure, using both, specific knowledge about the type of charges present within the biopolymer, as well as parameters such as pH and conductivity. Further, intentional changes are made to the pH and conductivity by introducing specific (counter) ions that are known to influence the thermodynamic stability of the biopolymer in solution. These include both, changes to the conformation of the biopolymers coils due to electrostatic interactions, as well as intermolecular interactions between neighbouring biopolymer coils due to the formation of (weak→ strong) physical bonds. Naturally, the accompanying changes to the structural conformations has an predictable influence on the properties of the biopolymer solution, which in this case is captured using rheology, i.e. the deformation of (solid, liquid and viscoelastic) materials due to the application of a load.

Specifically, rheology is used to track changes to the following parameters, the intrinsic viscosity: which is a measure for the size of the dissolved macromolecules, the Herschel-Bulkley consistency index: which is a measure for the viscous dissipation of concentrated biopolymer solutions, and the storage modulus and the yield stress. These latter two parameters collectively provide quantitative insight about the packing of weakly bonded biopolymer gel particles. In turn this information, i.e. changes to the rheological properties of a wide variety of representative biopolymer systems, is used to derive relevant structure-property relationships that may be exploited for engineering applications.

Finally, the collective insight gained by establishing these structure-property relationships is condensed to provide a simple rheology experiment. This simple experiment is practically relevant to ensure the on site quality of novel biopolymer formulations, as well as to aid suitable modifications to the existing extraction protocol.

The use of the consistency index, as determined from fitting rheological data to the Herschel–Bulkley model, is described such that it may yield systematic trends that allow a very convenient description of the dissipative flow properties of linear and branched (bio)polymers in general, both in molecular and weakly associated supramolecular solutions. The effects of charge-mediated interactions by the systematic variation of the ionic strength and hydrogen bonding by a systematic variation in pH, using levels that are frequently encountered in systems used in practice, is investigated. These effects are then captured using the associated changes in the intrinsic viscosity to highlight the above-mentioned trends, while it also acts as an internal standard to describe the data in a concise form. The trends are successfully captured up to 100 times the polymer coil overlap and 100,000 times the solvent viscosity (or consistency index). These results therefore enable the rapid characterization of biopolymer systems of which the morphology remains unknown and may continue to remain unknown due to the wide-ranging monomer diversity and a lack of regularity in the structure, while the macromolecular coil size may be determined readily.

A theoretical approach is presented to quantify the effect of ionic strength on the swelling and shrinkage of the hydrodynamic coil size of a generic biopolymer. This was conducted in view of extraction methods that often utilize acids and alkali combinations and, therefore, invariably impact the levels of salt found in commercially available biopolymers. This approach is supplemented by intrinsic viscosity measurements for the purpose of validation across a variety of biopolymer architectures, type of functionalization, as well as the quoted molar mass. By accurately capturing the magnitude of change in the coil size, it is discussed how a biopolymer coil size is far more sensitive to changes in the ionic strength than it is to the molar mass (or contour length) itself. In turn, it is highlighted why the current characterization strategies that make use of weight-averaged molar mass are prone to errors and cannot be used to establish structure—property relationships for biopolymers. As an alternative, the scope of developing an accurate understanding of coil sizes due to changes in the “soft” interactions is proposed, and it is recommended to use the coil size itself to highlight the underlying structure—property relationships.

Kaumera are extracellular polymeric substances (EPS) extracted from excess aerobic granular sludge from Nereda® wastewater treatment plants. Kaumera exhibits significant market potential across diverse applications, fostering rapid research and business development. Furthermore, it will begin to be extracted from numerous installations worldwide. This calls for standard methods as analogue to (waste)water and sludge characterization. Due to lack of standardization, stakeholders are currently using different extraction and characterization protocols, impeding the development of a more uniform product and comparison of results across research studies. To address this, this report compiles the standard protocol for Kaumera extraction in the laboratory and for on-site and lab characterization to be used by researchers, the public Dutch water authorities, and the private industry. The procedures detailed in this document are in accordance with EPS research conducted at TU Delft and methodologies employed in Kaumera production facilities. This report aids in monitoring Kaumera characteristics worldwide and for optimizing the extraction process (including up and downstream processing). This will help maximize repeatability, interoperability, and quality and therefore accelerate business and research development, paving the way to develop a product that meets the needs of the endusers. Through the widespread adoption of this manual, our aim is to foster greater coordination and collaboration among stakeholders, thereby expediting the realization of Kaumera's full potential.

The alginate montmorillonite (Alg-MMT) nanocomposite is a promising material for use in heat shields within space flight. The material can be produced as foams, which have a high thermal resistance. Before considering their implementation in heat shields, it is important to determine other mechanical properties as well. The aim of this study is to research whether the Alg-MMT nanocomposite foam is suitable for implementation in a heat shield for sounding rockets. Foams with varying densities as well as different configurations of sandwich structures are produced and evaluated. In order to get an insight into the mechanical behaviour of the foams and sandwich structures, double-lap shear tests and three-point bending tests are performed. The collected mechanical properties indicate that select configurations implementing the Alg-MMT foam can be used in a heat shield.