Microwave-assisted liquefaction of wood with polyhydric alcohols and its application in preparation of polyurethane (PU) foams

Abstract

Microwave radiation was used as the heating source in southern pine wood liquefaction with PEG/ glycerin binary solvent. It was found that microwave heating was more efficient than conventional oil bath heating for wood liquefaction. The wood residue content of the H 2 SO 4 catalyzed liquefied wood dropped to zero within 5 min with microwave heating. The resulting liquefied wood polyols have suitable hydroxyl values for the preparation of rigid PU foams. Both the compressive strength and apparent modulus of the liquefied-wood-based PU foams increased as the isocyanate index increased from 80 to 120. The foams from H 3 PO 4 catalyzed polyols had lower densities than those from H 2 SO 4 and the petroleum-based controls. They also showed lower strength and modulus than those from H 2 SO 4 . Liquefied-wood-based PU foams generally have lower compressive strength and apparent modulus than the petroleumbased controls. However, they showed better restorability from deformation than the petroleum-based controls. Zusammenfassung Mittels Mikrowellenstrahlung als Wär-mequelle wurde Southern Pine Holz mit PEG/Glycerin als binärem Lösungsmittelsystem verflüssigt. Es zeigt sich, dass Holz mittels Mikrowellenerhitzung effizienter verflüssigt werden kann als mittels konventioneller Erhitzung im Ölbad. Der Restholzanteil des mit Katalysator H 2 SO 4 verflüssigten Holzes fiel nach fünfminütiger Mikrowellenbeheizung auf Null. Die Hydroxylzahlen der so verflüssigten Holzpolyole sind für die Herstellung von PUHartschaumstoff geeignet. Sowohl die Druckfestigkeit als auch die Steifigkeit der PU-Schaumstoffe aus verflüssigtem Holz nahmen mit steigendem Isocyanatindex von 80 auf 120 zu. Die Schaumstoffe der mit Katalysator H 3 PO 4 erzeugten Polyole wiesen geringere Dichten auf als diejenigen mit Katalysator H 2 SO 4 und als Schaumstoffe auf Mineralölbasis. Die Festigkeit und der E-Modul waren ebenfall geringer. PU-Schaumstoffe auf Basis von verflüssigtem Holz wiesen generell eine niedrigere Druckfestigkeit und eine niedrigere Steifigkeit auf als die Kontrollproben auf Mineralölbasis. Allerdings zeigten sie ein besseres Rückverformungsverhal-ten als die Kontrollproben auf Mineralölbasis.

Acid Liquefaction of Potato (Solanum tuberosum) and Sweet Potato (Ipomoea batatas) Cultivars Peels – Pre-Screening of Antioxidant Activity/Total Phenolic and Sugar Contents

“…3). This phenomenon is already well-described for these types of processes, and are commonly associated with recondensation reactions or decomposition products (Hassan and Shukry 2008;Pan et al 2012;Dos Santos et al 2015). The highest conversion yields were 93% and 85% for potato peel and sweet potato peel, respectively.…”

Microwave-assisted Liquefaction of Cork - From an Industrial Waste to Sustainable Chemicals

“…On the other hand, the stretching band of C=O is clearly stronger in microwave assisted liquefaction than that for other procedures. This band indicates a higher content of carbonyl function resulting from the oxidation of hydroxyl groups [21,26,27]. Along with decreased hydroxyl number this results supports that oxidation reactions are indeed favored by microwaves.…”

“…The lower hydroxyl number obtained for product obtained from the microwave driven liquefaction, can be inferred to the oxidation since microwaves are able to promote more efficiently those reactions as well as recondensation reactions between the liquefaction solvents and cork components which consumed plenty of hydroxyl groups [21,24]. The specific composition of cork itself can also justify the lower values.…”

“…After 5 minutes, the conversion yields were already higher than 92%, reaching its higher value for the irradiation power of 300 W. Although for longer reactions, tar-type content appeared resulting in a small increase of the liquefaction residue. This could be attributed to recondensation reaction or decomposition products [20,21]. The liquefaction promoted by microwaves was also faster than that assisted by ultrasounds.…”

Factors Influencing Polyol Liquefaction of Nut Shells of Different Camellia Species

“…Various biomasses, such as bamboo (Aysu and Küçük 2013), crop residues (Hassan and Shukry 2008;Wei et al 2013), barks (D'Souza and Yan 2013), sawdust (Hui et al 2012), poplar (Li et al 2008), bamboo shells (Li 2014), bagasse (Ting et al 2007), and palm shells (Omoriyekomwan et al 2016), have been used as raw materials for liquefaction. Liquefying agents reported so far include phenol, polyethylene glycol, glycerin, ethylene glycol , ethylene carbonate (Xie and Chen 2005), and ionic liquids (Xie and Shi 2006;Zheng et al 2014).…”