Open Access

This study examines the dual benefits of microalgae cultivation for wastewatertreatment and the enhancement of polylactic acid-based biocomposites. UsingDesmodesmus sp. in a photobioreactor, both batch and continuous operationsachieve total nitrogen (TN) and total phosphorus (TP) removal rates of up to99.9%, maintaining TN and TP levels below 0.02 mg L−1 in the effluent, aligningwith European discharge standards. Continuous cultivation increases biomassproductivity from 0.102 to 0.43 g L−1 day−1 , a 322% improvement over batchoperations. Nutrient starvation followed by reintroduction to nutrient-richwastewater induces hyper-compensation luxury uptake, with P-enrichedcells accumulating 1.33% intracellular P within six hours — 21% higherthan natural accumulation. The results reveal that luxury phosphorus uptakein microalgae follows a triphasic system of uptake and storage, challengingthe previously suggested biphasic model. When incorporated into Poly lacticacid (PLA), the biomass enhances versatility, offering potential replacementof inorganic P in industrial applications, particularly flame retardants.Pyrolysis and cone calorimetry confirm the thermal and fire-retardantbenefits, with a 20% reduction in peak heat release rate and increased charyield. This work highlights microalgae’s role in sustainable biocomposites,supporting wastewater treatment, nutrient recovery, and CO2 sequestration.

Revolutionizing our polymer industry for adaption to a sustainable carbon circular economy has become one of today’s most demanding challenges. Exploiting renewable resources to replace fossil-fuel—based plastics with biopolymers such as poly(lactic acid) (PLA) is inevitable while using waste streams as a raw material resource at least is promising. When it comes to using PLA as technical polymer, its high flammability must be addressed by flame retardants compatible with the thermoplastic processing of PLA and its compostability. This study proposes microalgae enriched with phosphorus from wastewater (P-Algae) as an elegant way towards a kind of sustainable organophosphorus flame retardant. The concept is demonstrated by investigating the processing, pyrolysis, flammability, and fire behavior of PLA/P-Algae, while varying the P-Algae content and comparing P-Algae with four alternative bio-fillers (phosphorylated lignin, biochar, thermally treated sewage sludge, and metal phytate) with different P-contents as meaningful benchmarks.

A strategy for enhancing the sustainable flame retardancy of polylactide (PLA) composites by partially replacing melamine polyphosphate (MPP), a commercial flame retardant proposed for PLA, with wastewater polyphosphate-enriched microalgae (P-Algae) has been explored. The incorporation of P-Algae at a 1:1 ratio with MPP leads to a notable synergistic effect, surpassing the expected additive behavior of the individual components. Comprehensive characterization encompassing thermogravimetric analysis coupled with FTIR, pyrolysis combustion flow calorimeter (PCFC), cone calorimeter, oxygen index (LOI), UL-94 tests, and rheological measurements—demonstrates that the presence of this biomaterial can significantly enhance flame retardant performance. Replacing 50% of MPP with P-Algae in PLA resulted in a 17% reduction in peak heat release rate (pHRR) and maintained a V-0 rating in UL-94 testing. The use of P-Algae does not compromise the flame retardancy of PLA but rather contributes positively, offering a promising path toward more sustainable flame-retardant systems. By leveraging naturally derived biomass, this approach aligns with the growing demand for novel eco-friendly technologies in polymer engineering. Insights into an innovative renewable additive as a functional and effective component in flame-retardant biocomposites have been achieved.

Main message: We propose a combination of natural biomass from algae species Desmodesmus sp.along with commercially available flame retardant Melapur200 (melamine polyphosphate) in different mass ratios. We have successfully demonstrated that the use of both of them in PLA matrix biocomposites shows a synergistic flame retardant effect. Introduction: Poly(lactic acid) (PLA), a biodegradable polymer produced from renewable resources such as corn starch and sugarcane, is increasingly being used as a substitute for traditional petrochemical-based polymers in various commercial applications. However, its flammability characteristics need improvement to enable its use as a technical polymer. Based on previous successful experiments on PLA biocomposites with phosphor-enriched algae as filler [1], it was even mandatory to continue with enhancement of PLA flame retardancy. Therefore, tests for PLA biocomposites with P-algae containing melamine polyphosphate at different mass ratios were performed. Pyrolysis, reaction to small fire and fire behavior tests were carried out. Results and Discussion: Thermal stability analyses showed that all composites decompose earlier at lower temperature than pure PLA to a small extent. The evolved gases analysis revealed the release of ammonia and phosphates for the composites tested. PCFC analysis showed the greatest decrease in pHRR for the sample containing Melapur200/Algae (Figure 1A). Similarly, in the fire behaviour analysis, the best result was obtained for the sample containing a mixture of Melapur200 and Algae (Figure 1B). Satisfying results were obtained in the tests of reaction to small flame, where all the samples passed the classification from V-2 to V-0 (in the UL 94 test) and the oxygen index for the best sample was 27.4 +- 0.2%. When only Melapur200 or algae are added separately, a slight flame retardant effect is visible, however if both materials are added in suitable mixtures to the polymer, a synergistic effect is observable. In some cases, it can even be observed that the synergistic effect has surpassed expectations from the superposition. In conclusion, the combination of Melapur200 together with microalgae gives satisfying flame retardant effects for PLA biocomposites. Acknowledgement: The authors thank Dr. Georgios Mourgas (Tecnaro GmbH), and Dr. Michael Schweizer (Tecnaro GmbH) for their contributions to conceptualizing the project, raising the grant, and supporting this work. Thanks to Dr. Robert Gleuwitz (formerly of the BAM), Dr. Claudia Thomsen (iSeaMC GmbH) and Prof. Dr. Laurenz Thomsen (formerly of Jacobs University Bremen, now University of Gothenburg), Thanks to the financial support of the Bundesministerium für Bildung und Forschung – BMBF: KMU-innovativ: Biooekonomie 031B1289B

The multiphoton lithography (MPL) technique represents the future of 3D microprinting, enabling the production of complex microscale objects with high precision. Although the MPL fabrication parameters are widely evaluated and discussed, not much attention has been given to the microscopic properties of 3D objects with respect to their surface properties and time-dependent stability. These properties are of crucial importance when it comes to the safe and durable use of these structures in biomedical applications. In this work, we investigate the surface properties of the MPL-produced SZ2080 polymeric microstructures with regard to the physical aging processes during the post-production stage. The influence of aging on the polymeric microstructures was investigated by means of Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS). As a result, a time-dependent change in Young’s Modulus, plastic deformation, and adhesion and their correlation to the development in chemical composition of the surface of MPL-microstructures are evaluated. The results presented here are valuable for the application of MPL-fabricated 3D objects in general, but especially in medical technology as they give detailed information of the physical and chemical time-dependent dynamic behavior of MPL-printed surfaces and thus their suitability and performance in biological systems.