Delignification of wood pulp by hot alkali treatment following NO2/O2 pretreatment

Summary An effective delignification of kraft pulp without serious depolymerization of the cellulose was achieved by alkali treatment above 100°C, following pretreatment with NO₂/O₂ at approximately 50°C. Compared at the same degree of delignification the depolymerization of the carbohydrates and the yield were less than after oxygen bleaching of the pretreated pulp.     

Statistical regularities in vocabulary guide language acquisition in connectionist models and 15-20-month-olds.

This research tested the hypothesis that young children's bias to generalize names for solid objects by shape is the product of statistical regularities among nouns in the early productive vocabulary. Data from a 4-layer Hopfield network suggested that the statistical regularities in the early noun vocabulary are strong enough to create a shape bias, and that the shape bias is overgeneralized to nonsolid stimuli. A 2nd simulation suggested that this overgeneralization is due to the dominance of names for shape-based categories in the early noun vocabulary. Two subsequent longitudinal experiments tested whether it is possible to create word learning biases in children. Children 15-20 months old were given intensive naming experiences with 12 noun categories typical of the types of categories children learn to name early. The children developed a precocious shape bias that was overgeneralized to naming nonsolid substances; they also showed accelerated vocabulary development. Children taught an atypical set of nouns or no new nouns did not develop a shape bias and did not show accelerated vocabulary development. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Carbohydrate stabilization in wood by quinones and oxygen

Summary Spruce meal, impregnated with magnesium sulfate to suppress the depolymerization of the carbohydrates by oxygen, was treated with 1 M sodium hydroxide at 100°C in the presence of anthraquinone (AQ) or anthraquinone-2-sulfonic acid (AMS). A decreased loss of carbohydrates obtained in the presence of oxygen is related to an increased conversion of the reducing sugar end groups to aldonic acid end groups. Larger effects of oxygen were obtained with AMS compared to AQ.     

End-wise degradation of hydrocellulose during hot alkali treatment

Determinations of reducing and carboxylic acid end groups in hydrocellulose treated with hot alkali showed that the end-wise degradation proceeded to such an extent that some of the molecules were brought completely into solution. The major carboxylic acid end groups formed in reactions competing with the end-wise degradation were 3-deoxyhexonic and 2-C-methylglyceric acids; but 2-deoxypentonic, 2-C-methylpentonic, and minor amounts of aldonic acids were also formed. The formation of these stable end groups explains the observed increase in number average degree of polymerization during the treatment. The ratio between the number of lost glucose moieties and the number of carboxylic acid groups formed in the solid phase was about 170 and was only slightly affected by the duration of the hot alkali treatment.     

Dissolution of Lignin from Kraft Pulp after Treatment with Nitrogen Oxides

Laboratory experiments show that pretreatment with NO₂ including heating and ripening at 5% consistency and 90°C for 3 hours in the presence of NO₃- and H⁺ led to a dissolution of approximately 50–60% of the lignin in unbleached kraft pulp. Only 5–15% were dissolved when the treatment was terminated after heating to 90°C. An extensive fragmentation of the lignin during the ripening explains the extensive delignification in acid medium.

Fractionated dissolution of the remaining lignin by alkaline extraction gave fractions with small variation in N-contents (2.9–3.4%) and hydrophilicity. The last fraction exhibited the highest sorption of water vapor. The delignification was related to the decrease in molecular size during the pretreatment and during the subsequent alkaline treatments.     

Endwise degradation of hydrocellulose in bicarbonate solution

Determinations of individual terminal carboxylic acid endgroups and terminal reducing sugar moieties together with analysis of spent liquor revealed that the same reactions occur during treatment of hydrocellulose with hot sodium bicarbonate as with sodium hydroxide solution. Some fragmentation reactions, of little importance in the presence of sodium hydroxide, are favored in bicarbonate medium while benzilic acid rearrangements are less favored. Hence, the formation of 2-dieoxyerythropentonic acid endgroups is more important. Among the soluble reaction products, 3,4-dideoxypentonic acid formed via 3-deoxypentulose and cyclic compounds formed via the same precursor are much more abundant in bicarbonate medium while 3-deoxy-2-hydroxymethylpentonic (isosaccharinic) acids are less abundant.     

Carbohydrate stabilization with anthraquinone during alkaline pulping

Summary Treatment of wood meal with aqueous alkali in the presence of anthraquinone at 80°C leads to a conversion of reducing hexose end groups in the polysaccharides to mannonic and gluconic acid end groups. Xylose end groups are oxidized to xylonic and lyxonic acid groups. This leads to a stabilization of the polysaccharides against endwise alkaline degradation.     

On the growth of gallium phosphide layers on gallium phosphide substrates by MOVPE

We have investigated the growth and luminescence of gallium phosphide layers grown by MOVPE at atmospheric pressure using trimethylgallium and phosphine in a hydrogen ambient. Both the morphology and the type of luminescence were found to be strongly dependent on growth conditions. Hexagonal defects are observed on the epitaxial surfaces, changing to rhombic defects when the growth takes place with a low V/III ratio. The origin of these defects is stacking faults. The density of these defects is dependent on the growth temperature. Photoluminescence studies at 2 K were also carried out. In the bound exciton spectrum of the gallium phosphide layers, the silicon impurity appears on the gallium site with sufficient phosphine excess and at sufficiently high growth temperatures. A deep impurity level, related to silicon on a phosphorus site, is present when growth takes place with a low phosphine excess. We explain all observations by a model that implies that the growing surface can be either gallium-rich (resulting in phosphorus vacancies) or phosphorus-rich, resulting in gallium vacancies. The phosphorus-rich surface enables smooth epitaxial layers to be grown. With growth taking place at a phosphine to trimethylgallium ratio greater than 2.5, the surface is in a configuration stabilized by phosphorus reconstructions.