{"id":14851,"date":"2026-05-05T08:54:00","date_gmt":"2026-05-05T08:54:00","guid":{"rendered":"https:\/\/www.proefschriftmaken.nl\/portfolio\/julian-engelhardt\/"},"modified":"2026-05-05T08:54:19","modified_gmt":"2026-05-05T08:54:19","slug":"julian-engelhardt","status":"publish","type":"us_portfolio","link":"https:\/\/www.proefschriftmaken.nl\/en\/portfolio\/julian-engelhardt\/","title":{"rendered":"Julian Engelhardt"},"content":{"rendered":"","protected":true},"excerpt":{"rendered":"","protected":true},"author":7,"featured_media":14852,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_acf_changed":false,"footnotes":""},"us_portfolio_category":[45],"class_list":["post-14851","us_portfolio","type-us_portfolio","status-publish","post-password-required","hentry","us_portfolio_category-new-template"],"acf":{"naam_van_het_proefschift":"Taking Plastics with a Pinch of Salt","samenvatting":"Het aangaan van de uitdaging van de voortdurend groeiende hoeveelheid plastic afval en de impact ervan op het milieu vereist niet alleen betekenisvolle veranderingen in de manier waarop we materialen consumeren, verwerken en waarderen, maar ook een doordachte heroverweging van het materiaalontwerp. Materialen gebaseerd op polyelektrolytcomplexen hebben de potentie om hoge prestaties te combineren met ecologische duurzaamheid. Huidige voorbeelden bestaan echter vaak uit fossiele en op vinyl gebaseerde polyelektrolyten waarbij water en zout nodig zijn om de geladen groepen te weekmaken. Dit proefschrift onderzoekt nieuw ontworpen polyelektrolyten op basis van polyester, van synthese tot materiaalvorming en karakterisering, en stelt mogelijke toepassingen voor.\n\nHoofdstuk 1 schetst de vereisten en het potentieel van op polyester gebaseerde saloplastics als een duurzaam circulair materiaal met een gedefinieerd end-of-life scenario. Het belangrijkste voordeel ten opzichte van conventionele plastics is de on-demand, door zout geactiveerde oplossing na lekkage in de oceaan. Bovendien kan het gebruik van (bio-gebaseerde) polyesters bijdragen aan een potentieel afbreekbare ruggengraat.\n\nDit werd in Hoofdstuk 2 aangepakt door smeltpolycondensatie van gedeeltelijk bio-gebaseerde bouwstenen te gebruiken. Om beperkingen zoals hoge viscositeit te overwinnen, werden neutrale polyesters gefunctionaliseerd om geladen groepen te introduceren. Dit resulteerde in een kneedbaar materiaal met een glasovergangstemperatuur (Tg) van ~50 \u00b0C zonder extra weekmakers. De salopolyester kon worden gerecycled bij temperaturen vanaf 60 \u00b0C en bleek binnen 30 minuten volledig te ontbinden in een zeewaternabootsing.\n\nIn Hoofdstuk 3 werd ringopeningspolymerisatie gebruikt om polyelektrolyten met een gelijke polymerisatiegraad te verkrijgen, wat een dieper inzicht gaf in het effect van de architectuur op het complexatiegedrag en de zoutbestendigheid. Hoofdstuk 4 bouwde hierop voort door de negen resulterende droge complexen warm te persen zonder weekmaker. Er werd een sterke correlatie gevonden tussen de ladingsdichtheid en de Tg. Door de relatieve vochtigheid te vari\u00ebren, kunnen de eigenschappen worden afgestemd van bros tot elastomeer.\n\nHoofdstuk 5 geeft een overzicht van de verschillende gevolgde synthesestrategie\u00ebn, waarbij post-functionalisering van neutrale polymeren als de meest elegante methode naar voren kwam. Hoofdstuk 6 beoordeelt tenslotte hoe de ontwikkelde salopolyesters voldoen aan duurzaamheidscriteria en stelt toekomstige verbeteringen voor, zoals het introduceren van aromatische groepen.\n\nConcluderend zijn in dit proefschrift twee verschillende typen salopolyesters ontwikkeld voor complexvorming. De materialen zijn recyclebaar en vallen uiteen bij verhoogde zoutconcentraties. Waar de eerste generatie nog gevoelig was voor vochtigheid, bood de tweede generatie verbeterde mechanische sterkte en een hogere zoutbestendigheid. Deze op polyester gebaseerde complexen bieden een veelbelovende route naar duurzame en recyclebare kunststoffen.","summary":"Meeting the challenge of the continuously growing amount of plastic waste and its impact on the environment calls not only for meaningful changes in how we consume, dispose of, and value materials, but also for a thoughtful reconsideration of material design. Materials based on polyelectrolyte complexes may have the potential to combine high performance with environmental sustainability. However, current examples consist of fossil- and vinyl-based polyelectrolytes where water and salt are required to plasticize the charged moieties. This thesis explores newly designed polyester-based polyelectrolytes from synthesis toward material formation and characterization, and suggests potential applications.\n\nChapter 1 outlines the requirements and potential of polyester-based saloplastics as a sustainable circular material with a defined end-of-life scenario. The main advantage compared to conventional or other biobased\/biodegradable plastics is the on-demand, salt-triggered dissolution, after leaking into the ocean(s). Additionally, the involvement of (bio-based) polyesters can complete the picture of also incorporating a potential degradable backbone. The first challenge drafted was to establish a suitable synthesis route for such polyester-based polyelectrolytes to yield salopolyesters.\n\nThis was addressed in Chapter 2 by employing melt polycondensation of partly bio-based building blocks, yielding polyester-based polyelectrolytes. However, the use of charged monomers was found to result in a high melt viscosity and monomer degradation at elevated temperatures. To overcome these limitations, melt-obtained, neutral polyesters were functionalized to introduce charged moieties. The aliphatic nature of the polyelectrolytes and their low charge density, compared to conventional vinyl-based polyelectrolytes, resulted in a malleable material with a glass transition temperature (Tg) of ~50 \u00b0C, upon complexing, hot-pressing, and drying, without plasticization by water or salt. Moreover, the salopolyester could be recycled even at temperatures as low as 60 \u00b0C and was, overall, less brittle than the corresponding vinyl-based complexes. The salopolyester was found to fully decomplex in a seawater mimic (0.6 M NaCl) within a timeframe of 30 min. Overall, in their dry state, salopolyesters exhibit a unique combination of saloplastic and thermoplastic properties.\n\nBuilding on the promising results of this first generation of (partly) bio-based salopolyesters, we then aimed to obtain polyanions and polycations of equal degree of polymerization to prepare well-defined polyelectrolyte complexes. The ring-opening polymerization approach described in Chapter 3 turned out to be an efficient way to achieve this, allowing us to dive deeper into understanding the effect of polyelectrolyte architecture on the complexation behavior and complex properties, including salt resistance. Controlling the charge density and hydrophobic loading of three polyanions and three polycations resulted in a series of nine salopolyesters, which were analyzed in detail in their liquid state. A non-monotonic dependence of the critical salt resistance on the charge density was observed in either charge-dominated or hydrophobic-dominated regimes. Theoretical modeling accounting for electrostatic and non-electrostatic interactions aided in interpreting these trends. Ultimately, further development of this systematic approach could enable the selective tuning of specific salt resistances for target application materials.\n\nAdvancing this research direction, the availability of the six well-defined building blocks was further leveraged in Chapter 4 by hot pressing all nine dried complexes without the addition of any plasticizer. The resulting transparent, solid specimens were subjected to comprehensive thermomechanical analyses. Dynamic mechanical analysis and differential scanning calorimetry revealed a strong correlation between charge density and the glass transition temperature of the solid materials. Generally, by increasing the relative humidity, the mechanical properties of the complexes can be tuned from brittle to elastomeric. Interestingly, polyesters with lower charge densities were found to exhibit higher strain at break and even display ductile behavior under dry conditions. The interplay between charge density and hydrophobicity proves to be a powerful strategy for tuning material properties in overcoming the inherent brittleness of polyelectrolyte complexes, even under dry conditions. Furthermore, their performance was compared to that of conventional established plastic materials.\n\nChapter 5 provides an overview of the different synthesis strategies explored throughout this thesis. It outlines different routes for synthesizing polyester-based polyelectrolytes, primarily from bio-based monomers, via melt or ring-opening polymerization. Post-functionalization of neutral polymers is emphasized as the most flexible and elegant method for generating charged polyesters. particularly for polymers obtained via melt polycondensation. Strategies for incorporating aromatic moieties to enhance rigidity and hydrophobicity in the polyesters are also included and discussed. Overall, selecting specific monomers allows the tuning of the final saloplastic material properties to meet the desired performance criteria.\n\nFinally, Chapter 6 critically assesses how the developed salopolyesters match the required material properties in terms of sustainability. It offers a careful evaluation of the chemicals involved and proposes greener alternatives where required. A promising avenue for future work is to focus on introducing aromatic moieties into the polymer backbone either during polymerization as (co)monomer, or through post-modification. Additionally, comprehensive biodegradation studies are essential to confirm the sustainable nature of salopolyesters.\n\nTo conclude, within this thesis, two distinct types of salopolyesters were developed and employed to complex formation. The resulting materials are recyclable and decomplex at elevated salt concentrations. While the 1st generation of salopolyesters, built from polyelectrolytes with short chain lengths and broad dispersity, exhibit high sensitivity towards humidity, the ring-opening-derived, well-defined 2nd generation of polyelectrolytes yielded complexes with improved mechanical strength, enhanced humidity resistance, and a significantly higher salt resistance. Therefore, as a one-sentence summary, it can be stated that polyester-based complexes offer a promising pathway toward sustainable and recyclable plastics, warranting further exploration.","auteur":"Julian Engelhardt","auteur_slug":"julian-engelhardt","publicatiedatum":"22 mei 2026","taal":"EN","url_flipbook":"https:\/\/ebook.proefschriftmaken.nl\/ebook\/julianengelhardt?iframe=true","url_download_pdf":"https:\/\/ebook.proefschriftmaken.nl\/download\/a35a64f4-9e0d-4ed2-89d1-d03c852e4d24\/optimized","url_epub":"","ordernummer":"18522","isbn":"978-94-6534-377-8","doi_nummer":"","naam_universiteit":"Wageningen University","afbeeldingen":14853,"naam_student:":"","binnenwerk":"","universiteit":"Wageningen University","cover":"","afwerking":"","cover_afwerking":"","design":""},"_links":{"self":[{"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio\/14851","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio"}],"about":[{"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/types\/us_portfolio"}],"author":[{"embeddable":true,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/users\/7"}],"replies":[{"embeddable":true,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/comments?post=14851"}],"version-history":[{"count":1,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio\/14851\/revisions"}],"predecessor-version":[{"id":14854,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio\/14851\/revisions\/14854"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/media\/14852"}],"wp:attachment":[{"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/media?parent=14851"}],"wp:term":[{"taxonomy":"us_portfolio_category","embeddable":true,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio_category?post=14851"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}