Development of biobased materials from renewable resources

Laburpena

Nowadays, the society is enormously dependent on fossil resources to produce derived chemicals and fuels, which makes that its consumption grows continuously. However, petroleum, carbon and natural gas have a finite character and its direct impact on the global warming by the emissions of greenhouse gases and other environmental issues is well known. Hence, the search and development of sustainable and renewable production routes of fuels and materials is mandatory. Biomass has been proposed as the most interesting alternative feedstock due to its renewable character and its potential for producing derived materials and fuels. This research work is focused on the production of biobased materials by environmentally friendly processes using mainly vegetable oils as raw material. Biopolyols and biolubricants are the main targets because of its great consumption and the low biodegradability and high environmental impact of their non-renewable petroleum-based homologous. In order to promote a versatile and economically interesting full process, the research started up with the transformation of two different vegetable oils (namely grape seed and high-oleic sunflower oil) into platform chemicals which would be used in subsequent steps. Firstly, grape seed oil was successfully epoxidized in presence of peracetic acid generated in situ. The obtained kinetic model indicated that moderate high temperatures (90 ºC) and short reaction times (1 h) are the optimal to minimize the effect of secondary reactions. Secondly, the viability of using DBSA as amphiphilic catalyst during the acid hydrolysis of vegetable oils was tested. The effect of temperature, reaction time and the concentrations of DBSA and water was determined through the experimental design technique. The results from the ANOVA test indicated the great influence of the temperature on the fatty acid content of the product. On the other hand, the influence of time was predicted to be almost negligible. Once that the platform chemicals were successfully obtained, the transformation into high added value products was studied. Firstly, the viability of the ring-opening reaction of oxirane groups contained in epoxidized grape seed oil to produce biopolyols was studied. In a first approach, NaN3 was used as ring-opening reagent, finding a covalent linkage among the azide group and the biopolyol. In this case, the obtention of a rigid polyurethane foam using exclusively the azidified polyol was possible, achieving a significant improvement of the thermal stability of the foam. In a second approach, H3PO4 was used as ring-opening agent. Similar to NaN3, the covalent linkage of phosphate groups was demonstrated by FTIR and 31P-RMN. Unfortunately, the obtention of polyurethane foams using exclusively the phosphorylated polyol was not possible and uniquely a 57 wt.% was successfully incorporated into the formulation. Finally, thermogravimetric and surface composition analyses revealed the formation of a phosphoro-carbonaceous protective layer. Respecting to the production of biolubricants, free fatty acids were used as main raw material on its synthesis through two different processes. On the one hand, the oligomerization of free fatty acids conduced to the formation of estolides. Among the different catalysts tested, HClO4 reported the best activity. Nevertheless, a subsequent esterification process in presence of methanol was required to ensure a full transformation of unreacted oleic acid into derived products, improve the characteristics of the lubricant phase and facilitate the purification of the product. The positive effect on the process of incorporate an ionic liquid was also demonstrated. On the other hand, the synthesis of oleic-based trimethylolpropane (TMP) esters via esterification between oleic acid (OA) and TMP in presence of an acid catalyst using a reactive distillation process was explored. After determining the suitability of methanesulfonic acid as catalyst among many other homogeneous ones, the influence of the molar ratio OA:TMP was studied. A large amount of by-products were obtained for OA:TMP molar ratios lower than 2.5. Nevertheless, using an OA:TMP molar ratio of 3.0 only unreacted OA was obtained as impurity when the in situ formed water was removed by using the reactive distillation system. A predictive mathematical model was developed to determine the influence of the presence of by-products, and more specifically the presence of different functional groups, on the viscosity of the lubricant. Finally, the viability of using Kraft lignin as additive in PEG-based lubricants was determined. A commercially available Kraft lignin (KL) was incorporated into poly(ethylene glycol)s (PEGs) of different molecular weights (200 and 300 Da) by means of an ultrasound-assisted treatment. Stable dispersions of PEG with a KL content up to a 40 wt.% were successfully prepared through this method. The measurements of the dynamic viscosity and the Ostwald-de Waele model revealed a deviation from a Newtonian behaviour towards a pseudoplastic one at temperatures below 30 °C and lignin contents higher than 35 wt.% due to the temperature-reversible formation of lignin aggregates. Finally, the kinematic viscosity of the lignin-containing lubricants at 40 and 100 °C was determined and used to calculate their viscosity index, which was found to undergo a maximum improvement of nearly 50 % compared to neat PEG upon addition of an optimized amount of lignin.