Rlease And Biological Treatment Of Anionic Trashes During The Recycling Of Oldnewsprint

Some dissolved substances which called anionic trashes such as pectic acids, lignin-like substances that released during the recycling of American 8# old newspaper were studied systematically in this thesis. The release mechanism of the anionic trashes during pulping and bleaching was firstly studied and the DS (Dissolved Substances) was determined by GC (Gas Chromatography) both qualitatively and quantitatively. This was followed by a study of the degradation of pectinesterase on pectin model. Finally, the effect of anionic trashes on the pulp properties was investigated.During the process of pulping, with the increase of NaOH, H₂O₂ dosage and the time of pulping, both the cationic demand and conductivity of DS were improved, together with an increase of the absorbance at 280 nm. Carbohydrate was characterized by GC and the results showed that the total amount of carbohydrate was increased, especially the xylose and galacturonic acid. The main carbohydrate released during pulping and bleaching was increased. Nine compounds of the carbohydrate components which were determined quatitively were: xylose, mannose, galacturonic acid, glucose, galactose, arabinose, 4-O-methyl glucuronic acid, rhamnose, glucuronic acid, with a maximum release of xylose. With no addition of sodium hydroxide and hydrogen peroxide, only at pure alkaline conditions, the release of carbohydrates increased from 16.22 mg/L to 32.18 mg/L. By addition of hydrogen peroxide, the release of carbohydrates was 43.77 mg/L. During the process of pulping, the effect of sodium hydroxide on the release of carbohydrates was more obvious than the hydrogen peroxide.Alkaline hydrogen peroxide bleaching further promoted the release of the DS. The increase of NaOH, H₂O₂ dosage and temperature would result in the increase of cationic demand, conductivity and absorbance during the bleaching of old newsprint deinked pulp, indicating the improvement of anionic trashes released. At the high dosage of NaOH, the content of anionic substances increased with the increase of H₂O₂ dosage. The release of galacturonic acids and oxidized lignin led to the increase of anionic trashes.The dissolution of the total carbohydrates increased significantly when the sodium hydroxide and hydrogen peroxide dosage increased. Raising the temperature of the bleaching could also promote the release of anionic trashes. The carbohydrate components by GC analysis were same as the component in pulping process. The most is the release of xylose, another was the release of galacturonic acid.With no addition of sodium hydroxide and hydrogen peroxide, compared with the pure sodium hydroxide conditions, the total carbohydrates increased from 17.72 mg/L to 84.38 mg/L. The dissolution of the components also increased. It could be deduced that at alkaline conditions, poly glucose-galactose mannose undertook the deacetylation reaction, and for poly galacturonic acid xylose, 4-O-methyl glucuronic acid arabinose xylose,β-elimination reaction occurred, at the same time, the rupture of lignin-carbohydrate ester bond between the LCC also promoted the release of carbohydrates. The alkaline hydrogen peroxide conditions further improved the release of carbohydrates. Compared to the pure alkaline conditions, the release of carbohydrates doubled from 84.38 mg/L to 169.69 mg/L. The significant release of galacturonic acid may be due to theβ-elimination reaction of pectin acid, so glycosidic bond fracture and which caused the release of galacturonic acid.Pectin models and DS was treated by pectinesterase and the results showed that the enzymatic treatment decreased the cationic demand significantly. Analysis by GPC (Gas gel permeation chromatography) for different enzyme dosage and the time of biotreatment showed that with the enzyme dosage increase, the relative molecular weight of degraded pectin decreased. With the increase of treating time, pectin models'relative molecular weight dropped significantly.Investigation on the effect of anionic trashes on pulp properties indicated that not only the brightness and strength properties were decreased by large amount of anionic substances, but the function of cationic additives was influenced. When the DIP was treated with pectinesterase, the cationic demand decreased and the drainage performance was improved. Meanwhile, the function of CPAM enhanced apparently. Significantly, the treatment of pectinase had no negative effect on the brightness and strength.