Kemijska reciklaža prožnih poliuretanskih pen

Grdadolnik, Maja (author), Žagar, Ema (mentor)

Poliuretani (PU) so nepogrešljivi materiali našega vsakdana. Več kot polovico PU materialov predstavljajo PU pene, kjer so prožne PU pene sestavni del oblazinjenega pohištva, toge PU pene pa uporabljamo predvsem kot toplotno in zvočno izolacijske materiale. Obsežna proizvodnja in uporaba PU pen vodita do naraščajočih količin odpadkov, s katerimi moramo ravnati v skladu z Evropskimi smernicami. Trajnostni pristop ravnanja z odpadnimi PU penami je kemijska reciklaža, ki omogoča pridobivanje recikliranih surovin, primernih za ponovno uporabo za sintezo PU pen ali drugih polimernih produktov. Cilj raziskovalnega dela je bil razviti metodo za učinkovito razgradnjo odpadnih, prožnih PU pen, različne kemijske sestave. V ta namen sem raziskala acidolizo in aminolizo kot metodi za razgradnjo karbamatnih vezi v strukturi PU pen. Pri tem sem uporabila različne reagente v različnih količinah in vodila reakcije pri različni temperaturi in času. Raziskala sem vpliv eksperimentalnih pogojev razgradnje PU pen na strukturne lastnosti recikliranih polieter poliolov in na tvorbo stranskih produktov. Konvencionalno segrevanje reakcijskih zmesi sem nadomestila z energijsko učinkovitejšim segrevanjem z mikrovalovi, ki skrajša izvedbo postopkov iz več ur na manj kot eno uro. Acidoliza PU pen z dikarboksilnimi kislinami je za industrijo obetajoča kemijska reciklažna metoda, ker razgradnja PU pen poteka z manjšimi količinami reagenta, kot je to v primeru razgradnje PU pen z obsežno raziskovano glikolizo. Razlog je v tem, da je acidoliza karbamatnih skupin ireverzibilna reakcija, pri kateri se sprosti ogljikov dioksid in nastane termično stabilna amidna vez. V nasprotju z acidolizo je glikoliza, kot najobsežneje raziskana metoda razgradnje PU pen, reverzibilna reakcija, zaradi česar moramo uporabiti velik presežek glikolnih reagentov, da reakcijo potisnemo v smer nastajanja produktov. Rezultati acidolize prožnih PU pen kažejo, da ne glede na izbrane eksperimentalne pogoje ne moremo pridobiti popolnoma hidroksilno terminiranega recikliranega polieter poliola, ki bi bil popoln ekvivalent originalnemu poliolu, saj pri manjših količinah uporabljene dikisline razgradnja karbamatnih skupin ni popolna, kar vodi do recikliranih poliolov, ki so delno funkcionalizirani z aromatskimi amini. Pri dovolj visoki količini uporabljenega reagenta lahko dosežemo visoko stopnjo razgradnje karbamatnih skupin (> 98 mol%), vendar na račun večje stopnje esterifikacije hidroksilnih skupin poliola z dikislino, kar vodi do delno karboksilno terminiranih recikliranih poliolov. Prednost acidolize pred ostalimi metodami je, da ima dikarboksilna kislina tudi funkcijo lovilca aminov, kar preprečuje nastanek neželenih aromatskih diaminov v procesu razgradnje PU pen. Aminoliza prožnih PU pen pri dovolj veliki količini uporabljenega tris(2-aminoetil)amina ali polietilenimina vodi do visoke stopnje razgradnje karbamatnih skupin (~ 99 mol%), kar pripisujemo katalitskemu učinku terciarne aminske skupine v strukturi istega reagenta. Iz tega razloga lahko učinkovito aminolizo PU pen s tris(2-aminoetil)aminom ali polietileniminom izvedemo z uporabo majhnih količin reagenta. Popolno razgradnjo karbamatnih skupin sem dosegla z dvostopenjsko aminolizo, kjer sem v prvi stopnji za razgradnjo prožne PU pene uporabila tris(2-aminoetil)amin ali cenejši heksametilendiamin, izolirala delno aromatsko aminski recikliran poliol, ki sem ga ponovno podvrgla aminolizi s tris(2-aminoetil)aminom. Reciklirane poliole z različno vrsto in vsebnostjo končnih skupin (aromatsko aminske, karboksilne in hidroksilne končne skupine) in hidroksilno funkcionaliziran recikliran poliol sem v nadaljevanju uporabila v različnih količinah za sintezo novih prožnih PU pen. Ugotovila sem, da predvsem karboksilne končne skupine in v manjši meri tudi aromatsko aminske končne skupine recikliranih poliolov negativno vplivajo na potek polimerizacije PU pen oziroma na relativno hitrost penjenja in zamreževanja, kar vpliva na celično morfologijo pen. Posledično so mehanske lastnosti prožnih PU pen iz recikliranih poliolov slabše v primerjavi s PU penami, sintetiziranimi iz originalnih poliolov. Dobre mehanske lastnosti prožnih PU pen, ob nespremenjenem katalitskem sistemu, sem dobila le z uporabo čiščenega, hidroksilno funkcionaliziranega recikliranega poliola, ne glede na to, koliko originalnega poliola sem v formulaciji nadomestila z recikliranim, kar pripisujem primerljivim strukturnim lastnostim (molska masa, vrsta končnih skupin) recikliranega in originalnega poliola in odsotnosti nizko-molekularnih stranskih produktov v recikliranem poliolu.

• Language: Slovenian
• Keywords: kemijska reciklaža, prožne PU pene, mikrovalovno segrevanje, acidoliza, aminoliza
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: FKKT - Faculty of Chemistry and Chemical Technology
• Year: 2024
• PID: 20.500.12556/RUL-154196
• COBISS.SI-ID: 183385091
• Publication date in RUL: 31.01.2024

Secondary language

• Language: English
• Title: Chemical recycling of flexible polyurethane foams

Abstract

Polyurethanes (PU) are indispensable materials in our everyday lives. PU foams account for more than half of PU materials, with flexible PU foams being an integral part of upholstered furniture, while hard PU foams are mainly used as thermal and sound insulation materials. The large-scale production and use of PU foams results in an increasing amount of waste that needs to be processed in accordance with European directives. A sustainable approach to dealing with PU foam waste is chemical recycling, which enables the recovery of recycled raw materials that can be reused for the synthesis of PU foams or other polymer products. The aim of the doctoral thesis was to develop a method for the effective decomposition of waste based on flexible PU foam of different chemical composition. For this purpose, acidolysis and aminolysis were investigated as methods for the degradation of carbamate groups in the PU foam structure. Different reagents were used in different amounts and the degradation experiments were performed at different temperatures and times. The influence of the experimental conditions used for degradation of PU foams on the structural properties of the recycled polyether polyols and on the formation of side products was investigated. Conventional heating of the reaction mixtures was replaced by more energy-efficient microwave heating, which shortened the procedures from several hours to less than one hour. Acidolysis of PU foams with dicarboxylic acids is a promising chemical recycling method from the industry’s point of view, as the degradation of PU foams takes place with smaller amounts of reagent than in the case of PU foam degradation by glycolysis. The reason for this is that the acidolysis of carbamate groups is an irreversible reaction, where carbon dioxide is released and a thermally stable amide bond is formed. In contrast to acidolysis, glycolysis as the most studied method for PU foam degradation is a reversible reaction, so the use of a large excess of glycolic reagents is required to drive the reaction towards product formation. The results of acidolysis of flexible PU foams show that, regardless of the experimental conditions chosen, we cannot obtain a fully hydroxyl-functionalized recycled polyether polyol that would be a perfect equivalent of the virgin polyol because, with small amounts of diacid used, the degradation of the carbamate groups is not complete, resulting in recycled polyols that are partially functionalized with aromatic amino end groups. With a sufficiently high amount of diacid reagent, a high degree of carbamate group degradation (> 98 mol%) can be achieved, but at the expense of a higher degree of esterification of the hydroxyl groups of the polyol with the diacid, resulting in partially carboxyl-terminated recycled polyols. The advantage of acidolysis over other methods is that the dicarboxylic acid also acts as an amine scavenger and prevents the formation of unwanted aromatic diamines during PU foam degradation. Aminolysis of flexible PU foams with a sufficiently large amount of the tris(2-aminoethyl)amine or polyethylenimine results in a high degree of degradation of the carbamate groups (~ 99 mol%), which is due to the catalytic effect of the tertiary amine group in the structure of the same reagent. For this reason, efficient aminolysis of PU foam can be performed with tris(2-aminoethyl)amine or polyethylenimine using small amounts of the reagent. The complete degradation of the carbamate groups in the PU foam structure was achieved with a two-step aminolysis, in which we used tris(2- aminoethyl)amine or cheaper hexamethylenediamine in the first step to degrade the flexible PU foam and isolate the recycled polyol partially functionalized with aromatic amino end groups, which was again subjected to an aminolysis process with tris(2-aminoethyl)amine. Recycled polyols with different types and contents of end groups (aromatic amino, carboxyl and hydroxyl end groups) and hydroxyl-functionalized recycled polyol were then used in different amounts for the synthesis of new flexible PU foams. The results show that especially the carboxyl groups and to a lesser extent the aromatic amino end groups of the recycled polyols have a negative influence in the course of PU foam polymerization, which is due to unbalanced cross-linking and foaming reactions that affect the cell morphology and ultimately lead to a deterioration of the mechanical properties of the synthesized flexible PU foams. Suitable mechanical properties of the flexible PU foams were obtained with an unmodified catalytic system only by using purified hydroxyl-functionalized recycled polyol, regardless of how much of the original polyol was replaced by recycled in the PU formulation. This is a consequence of the comparable structural properties (molar mass, type of end groups) of recycled and original polyol and the absence of low-molar mass side products in the recycled polyol.

• Keywords: chemical recycling, flexible PU foams, microwave heating, acidolysis, aminolysis