ABSTRACT
Incorporating biopolymers in packaging foams can contribute to a more circular packaging system, utilizing renewable and compostable materials. Gelatin, with its favorable physicochemical properties, allows for producing gelatin foams via mechanical foaming, a well-established and low-investment process. To improve foam properties, starch can be added to the gelatin formulation. However, the variability in the properties of starch powders can impact the polymer blend and, consequently, the properties of the dry foam. This study aimed to investigate the impact of different starch powders from different botanical origins (tapioca and corn) and treatments (native or pregelatinized) on the properties of gelatin-starch foams produced by mechanical foaming. The study successfully produced foams with densities of approximately 45-50 kg/m3 and compression properties comparable to EPS (expanded polystyrene) foams. The starch type and pre-treatment significantly influenced the properties of the foam. Pregelatinized starches exhibited slightly higher densities due to lower foamability caused by higher viscosity. Using starch exhibiting total loss of birefringence led to denser foams with greater compression properties than those with starch with a certain degree of crystallinity remaining. Therefore, selecting the appropriate starch type is crucial when developing starch-based materials to ensure optimal material and processing properties align with application requirements.
ABSTRACT
Gelatin hydrogels are widely used materials that may require surfactants to adjust their solution's surface tension for cell attachment, surface adsorption enhancement, or foaming. However, gelatin is a highly surface-active polymer, and its concentrated solutions usually do not require surfactants to achieve low surface tension. However, anionic surfactants, such as sodium dodecyl sulfate (SDS), interact strongly with gelatin to form complexes that impact its hydrogels' rheological properties, influencing processability and functionality. Nevertheless, there is a lack of systematic research on the impact of these complexes on high gelatin content (i.e., high strength) hydrogels' rheological properties. In this work, the SDS/gelatin ratio-dependent viscoelastic properties (e.g., gel strength, gelation kinetics, and melting/gelling temperature) of high-strength gelatin hydrogels were investigated using rheology and correlated to surface tension, viscometry, FTIR, and UV-Vis spectrophotometry. SDS-gelatin ratio was proved to be an important factor in tailoring the rheological properties of gelatin hydrogels. The gel strength, gelation kinetics, and melting/gelling temperature of the gelatin hydrogels linearly increased with SDS incorporation up to a maximum value, from which they started to decline. The findings of this work have wide applicability in tailoring the properties of gelatin-SDS solutions and hydrogels during their processing.
ABSTRACT
Plastic litter is encountered in aquatic ecosystems across the globe, including polar environments and the deep sea. To mitigate the adverse societal and ecological impacts of this waste, there has been debate on whether 'biodegradable' materials should be granted exemptions from plastic bag bans and levies. However, great care must be exercised when attempting to define this term, due to the broad and complex range of physical and chemical conditions encountered within natural ecosystems. Here, we review existing international industry standards and regional test methods for evaluating the biodegradability of plastics within aquatic environments (wastewater, unmanaged freshwater and marine habitats). We argue that current standards and test methods are insufficient in their ability to realistically predict the biodegradability of carrier bags in these environments, due to several shortcomings in experimental procedures and a paucity of information in the scientific literature. Moreover, existing biodegradability standards and test methods for aquatic environments do not involve toxicity testing or account for the potentially adverse ecological impacts of carrier bags, plastic additives, polymer degradation products or small (microscopic) plastic particles that can arise via fragmentation. Successfully addressing these knowledge gaps is a key requirement for developing new biodegradability standard(s) for lightweight carrier bags.
