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The ethanolic fermentation of liquid fractions (hydrolysates) issued from dilute acid pre-treatment of olive tree biomass by Pichia stipitis is reported for the first time. On the one side, P. stipitis has been reported as the most promising naturally occurring C5 fermenting microorganism; on the other side, olive tree biomass is a renewable, low cost, and lacking of alternatives agricultural residue especially abundant in Mediterranean countries. The study was performed in two steps. First, the fermentation performance of P. stipitis was evaluated on a fermentation medium also containing the main inhibitors found in these hydrolysates (acetic acid, formic acid, and furfural), as well as glucose and xylose as carbon sources. The effect of inhibitors, individually or in a mixture, on kinetic and yield parameters was calculated. In a second step, hydrolysates obtained from 1% (w/w) sulfuric acid pre-treatment of olive tree biomass at 190°C for 10 min were used as a real fermentation medium with the same microorganism. Due to inhibition, effective fermentation required dilution of the hydrolysate and either overliming or activated charcoal treatment. Results show that ethanol yields obtained from hydrolysates, ranging from 0.35 to 0.42 g/g, are similar to those from synthetic medium, although the process proceeds at lower rates. Inhibiting compounds affect the fermentation performance in a synergistic way. Furfural is rapidly assimilated by the yeast; acetic acid and formic acid concentrations decrease slowly during the process. Activated charcoal or overliming detoxification improve the fermentability of diluted hydrolysates.

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In this work several lignocellulose pulps from different origin and/or submitted to different treatments were crosslinked with hexamethylene diisocyanate (HMDI) and further dispersed in castor oil in order to obtain gel-like formulations based on renewable resources, which can be potentially applicable as semi-solid lubricants. The rheological and tribological properties attained as well as physical and mechanical stability were suitable to consider these gel-like dispersions as efficient alternatives to traditional lubricating greases. The rheological behavior was evaluated by means of both small-amplitude oscillatory shear tests (SAOS) and viscous flow measurements, at different temperatures. The HMDI/cellulose pulp weight ratio applied in the crosslinking reaction can be used to modify and modulate the consistency and the values of rheological functions of these gel-like dispersions. However, the rheological behavior is not qualitatively affected by the amount of HMDI used as coupling agent. The thermo-rheological response evidences a softening temperature of around 100ºC. Mechanical stability of HMDIcrosslinked lignocellulose-based oleogels, evaluated as the loss of consistency after submitting the sample to a working test, was significantly improved respecting the non-crosslinked lignocellulose gel-like dispersion. Microstructural morphology was examined using the atomic force microscopy (AFM) and consist of long and entangled fibers, extremely similar to that found in lithium greases. Moreover, friction coefficient and resulting wear mark diameters obtained in a ball-on-disc contact lubricated with these eco-friendly formulations were, in most cases, comparable to that obtained with commercial lubricating greases. Therefore, HMDIcrosslinked lignocellulose materials are proposed as effective and promising eco-friendly thickener agents in vegetable oils.