Isocyanate curing of novolac-type ligno-phenol–formaldehyde resins

This work proposes the use of a diisocyanate as curing agent for novolac-type lignin–phenol–formaldehyde (LPF) resins, instead of typical hexamethylene–tetraamine (HMTA), with the aim of overcoming the loss of reactivity of lignophenolic resins resulting from the introduction of lignin. Curing LPF resins with methylene–diisocyanate (MDI) and HMTA has been investigated through Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC) and rheological analysis. The analysis of experimental results shows that the proposed curing reaction with MDI gives similar results to those for HMTA-cured systems. However, MDI curing is faster than HMTA one and proceeds easier at lower temperatures.     

Chemical characterization of wood and extractives of fast-growing Schizolobium parahyba and Pinus taeda

This study aims to evaluate the chemical composition of wood and extractives of Pinus taeda and Schizolobium parahyba (guapuruvu) as potential feedstock for new applications in the biorefinery industry. For this purpose, their content of α-cellulose, hemicellulose, insoluble lignin, hot water solubility, NaOH_1% solubility, inorganic materials (ash), and monomeric sugars by high-performance liquid chromatography was quantified. Attenuated total reflectance infrared spectroscopy and thermogravimetric analysis were also used to complete the physicochemical characterization of the studied woods. The extractives were obtained by soxhlet extraction with ethanol:toluene and dichloromethane and identified with pyrolysis-gas chromatography/mass spectroscopy technique. The results showed that guapuruvu wood has the higher amount of hemicellulose (16%) when compared to pine wood (10%), which resulted in higher solubility in alkali solution. Furthermore, in relation to other biomasses, the two woods presented more percentage of lignin and minor content of hemicelluloses. The P. taeda wood presented the highest percentage of extractives mainly composed of fatty acids and aromatic hydrocarbons, while guapuruvu wood had a higher percentage of phenolic compounds and also fatty acids. Both the materials have low content of extractives with dichloromethane and were mainly composed of lipophilic compounds.     

Polyol production by chemical modification of date seeds

Polyol production from chemical modification of date seeds has been investigated through oxypropylation and liquefaction techniques (using organic solvents in the presence of a catalyst). The obtained products were characterized using infrared spectroscopy analysis, ¹H NMR, thermogravimetric analysis and other parameters such as hydroxyl number (I_OH) and viscosity. Results showed that 93% of the solid substance was converted into polyol in the oxypropylation reaction at the date seeds/propylene oxide ratio of 0.25 and 10% potassium hydroxide at 160 °C. The oxypropylated product has I_OH of 779 mg KOH/g and viscosity of 6.9 Pa s. Regarding the liquefaction technique, results show that a yield of 95% was obtained at the date seeds/liquefying solvent ratio of 0.25 in 60 min of reaction at 160 °C. The liquefied product shows I_OH of 336 mg KOH/g and viscosity of 0.9 Pa s.     

Efficacy of olive mill waste water and its derivatives in the suppression of crown gall disease of bitter almond

Olive mill waste water (OMW) and some of its indigenous bacterial strains were tested in vitro and in planta for their efficacy against crown gall disease caused by Agrobacterium tumefaciens. OMW and polyphenols displayed a high level of antibacterial activity, however the volatile fraction was less efficient as only a bacteriostatic effect was observed. In pot experiments, the percentage of bitter almond rootstock showing symptoms of crown gall was significantly reduced with the dosage rate of OMW 1% as compared to the control (highly natural infected soil treated with water). Five indigenous bacterial strains isolated from OMW exhibited an antagonistic effect against the bacterium. Based on the gene 16S rRNA sequence analysis, one isolate showed 99.2% similarity to known sequences of Bacillus subtilis, one isolate demonstrated high percentage similarities (99.3%) to the genera Bacillus pumilis, and two isolates were associated with Stenotrophomonas maltophilia and Pseudomonas putida 100% and 99.6% similarities respectively. Among these bacteria, the strain B1 proved efficient against the soil borne pathogen in vitro and pot experiments. Our study in controlled conditions suggested that the addition of OMW to soil exerts significant disease suppressiveness against A. tumefaciens. Thabet Yangui and Ali Rhouma contributed equally to this work and are regarded as joint first authors.     

Antioxidant activity of phenolic compounds obtained by autohydrolysis of corn residues

This study aimed to evaluate the effect of autohydrolysis temperature of corn residues in the antioxidant activity of the phenolic compounds extracted from the liquid phase. The treatments were carried out at 160, 180, 190 and 200 °C for 30 min in a pressurized batch reactor. Two different methods for phenolic compounds extraction from the autohydrolysis liquors were investigated. For that purpose, solvent extraction with ethyl acetate and acidic precipitation were performed for phenolic compounds recovery. These methods have been compared in terms of extraction yield, physicochemical properties of obtained polyphenols (characterization by Fourier Transform Infrared Spectroscopy, Thermogravimetric Analysis and Gel Permeation Chromatography), total phenolic content, total antioxidant capacity and Trolox equivalent antioxidant capacity (TEAC) values, measured in DPPH (2,2-diphenyl-1-picrylhydrazyl) test system. The maximum phenolic contents ranged from 6.04 mg GAE/100 mg extract in acidic precipitated samples to 16.45 mg GAE/100 mg extract in ethyl acetate soluble fractions. The results indicated that the ethyl acetate fractions possessed the highest antioxidant activity, reaching after 30-60 min the same capacity reported for the reference synthetic antioxidants (Trolox).     

Changes in nutrient concentrations and leaf gas exchange parameters in banana plantlets under gradual soil moisture depletion

Changes in mineral nutrient concentration, growth, water status and gas exchange parameters were investigated in young banana plants (Musa acuminata cv. ‘Grand Nain’) subjected to gradual soil moisture diminution. Experiments were performed in glasshouse under controlled temperature, and water stress was imposed by ceasing irrigation for 62 days. The data showed a parallel decrease of leaf gas exchange parameters and soil moisture initiated few days after the imposition of water stress. However, the leaf relative water content (RWC) showed a minor decrease in response to drought. The onset of growth reduction evaluated as plant height, pseudostem circumference, number of newly emerged leaves, leaf area, and leaf and root biomass took place approximately between 34 and 40 days after the beginning of the stress period. In addition, drought did not modify nitrogen and phosphorus concentrations in foliar and root tissues; however, it increased potassium, calcium, magnesium, sodium and chloride in leaves, and only calcium, sodium and chloride in roots. Collectively, the data reveal that banana plants show a drought avoidance mechanism in response to water stress. After a prolonged drought period, leaf RWC was hardly reduced, while gas exchange and growth parameters were reduced drastically. Increasing leaf mineral concentration could have help to maintain leaf RWC due to osmotic adjustment mechanism.     

Ameliorative Effect of Municipal Solid Waste Compost on the Biological Quality Of Mediterranean Salt Lake Soil

Different loads of municipal solid waste compost (MSWC) were applied to hyper saline salt lake soil under laboratory conditions to monitor biological soil quality. Microbial biomass-C (MBC), catalase, dehydrogenase, urease, alkaline phosphatase, arylsulfatase, and β-glycosidase activities were analyzed following 14, 30, and 50 days of incubation. In general, MBC and the oxidoreductase and hydrolase enzyme activities were significantly enhanced by addition of MSWC at 20 and 40 t ha^?1 doses, but they decreased at 120 t ha^?1. Overall, the results show that the addition of MSWC to hyper saline soils can improve soil biological quality, in spite of its high salt content, which is an important step in any attempt to use them as biosaline agricultural soils. However, substances such as heavy metals in MSWC could limit the use of compost for this purpose; consequently, analysis of MSWC is recommended prior to its use.     

Limits imposed by salt to the growth of the halophyte Sesuvium portulacastrum

The growth of the halophyte Sesuvium portulacastrum, commonly known as sea purslane, is impeded by NaCl only at high (600–1000 mM) concentration. Therefore, the goal of this investigation was to identify the mechanisms which set the limit of the salt resistance of S. portulacastrum. 21‐day‐old cuttings were grown for 45–50 d under split‐root conditions in which one half of the root system was immersed in complete nutrient solution supplemented with 800 mM NaCl, while the other half was immersed in a NaCl‐free medium, containing all nutrients or being deprived of potassium or calcium or nitrogen. Using this approach, we demonstrate that K⁺ and N uptake was impaired in roots exposed to NaCl. Concerning Ca²⁺, there was no indication of uptake inhibition by NaCl. However, restriction of K⁺ uptake by roots was compensated by an increase in the K⁺‐use efficiency, so that growth was not inhibited. Concerning N, our analysis shows that NO and/or NH uptake, but not their assimilation, was limited by salt treatment. Thus, we conclude that at high salinity levels, the growth of S. portulacastrum is limited by the restrictions imposed by NaCl on N uptake, perhaps in addition to inhibiting effects of excessive Na⁺ accumulation in shoot.