Effects of modification with melamine–urea–formaldehyde resin on the properties of urea pretreated eucalyptus

Eucalyptus urophylla was treated with melamine-urea-formaldehyde resin (MUF) after pretreatment with urea solution. The properties of the wood were then determined. The weight percent gain (WPG) and, antiswelling efficiencies (ASE) of the wood treated with urea+MUF were 14% and, 45% higher than those of untreated wood, respectively. The water absorption (WA) of the wood treated with urea+MUF was decreased approximately 50% lower than that of the untreated wood. However, the mechanical properties of the wood treated with urea+MUF were weakened due to the destruction of the structure of wood. An X-ray photoelectron spectroscopy (XPS) analysis revealed that the atomic concentration ratio of O/C was increased. The ratio of C1 was decreased as the lignin and extractives contents were decreased, while the ratios of C2 and C3 were increased. The urea solution pretreatment was conducive to the impregnation of wood functional modifiers.

Investigation of urea usage in soda pulping of Populus deltoides

In this study, the use of the urea was investigated as an additive in soda pulping of Populus deltoides in comparison with the conventional soda and Kraft processes. Urea was used at the ratios of 1.5%, 3%, 4.5%, and, 6% based on the dry weight of wood in the soda process. The constant factors were determined for each distinct cooking of soda, soda-urea, and Kraft treatments. The dry weight of the chips was 150 g, the ratio of the liquor to wood (L/W) 4: 1, the maximum temperature 170°C and active alkaline content 18% (based on Na2O). Cooking time, the only changing factor, was varied from 30 to 330 min depending on the type of cooking. Besides, the sulfidity ratio was 25% for all Kraft treatments. After ending pulping time, the pulp samples were fully washed. Then, the screen accepts and the screen rejects were evaluated using a 20 and a 200-mesh screen. The observation shows that the more urea usage is in a pulping liquor, the more total yield, however, the screen reject value unexpectedly increased. Hence, the optimum values were determined by 1.5% and 3%. The investigation of handsheet samples indicated an increment trend of mechanical strengths with an addition of urea; so that the tear, tensile, and burst indexes of soda-urea samples were significantly higher than for each symmetric soda sample. It has been supposed that cellulose carbamate is essential in the enhancement.